An incoming invoice is, to begin with, only a claim: someone states that they delivered, and names an amount. Whether the quantity is right, whether the price is the agreed one and whether the goods arrived at all is not in the invoice. It is in two other documents created in two other departments: the purchase order and the goods receipt posting. The three-way match lays these three documents on top of each other and checks field by field whether they agree. What agrees can be posted without anyone looking at it. What does not agree needs an owner, a deadline and a place where it stays visible. The difference between the two routes can be quantified: mean processing costs per incoming invoice are 15.69 euros; that figure comes from a 2017 data collection across four industry groups from manufacturing, utilities and services and is not specific to the Mittelstand (BME 2018). A mid-sized company receives an average of around 47 incoming invoices per month (IW Consult 2025). This article describes which fields are compared, how to build a tolerance band that does not turn every rounding difference into a case, and why input VAT deduction depends on an invoice that meets the statutory requirements (Umsatzsteuergesetz).
Key takeaways
- The match compares order, goods receipt and invoice field by field: article, quantity, price, terms. If all three agree, no human work is created; only the deviation produces a case.
- Processing one incoming invoice costs 15.69 euros on average; that was measured in 2017 across four industry groups from manufacturing, utilities and services, not in the Mittelstand (BME 2018). Together with an average of 47 incoming invoices per month in the German Mittelstand (IW Consult 2025) this gives an order of magnitude for accounts payable, not a cost calculation for your own company.
- Input VAT deduction requires an invoice issued in accordance with the statutory rules (Umsatzsteuergesetz). The mandatory particulars are therefore not a formality but the checklist the match has to work through anyway.
- A payment term of more than 60 days is only effective if it was expressly agreed and is not grossly unfair; a verification period of more than 30 days likewise requires an express agreement (Bürgerliches Gesetzbuch). Time spent waiting in the check is not a neutral state.
- Invoices must be retained for eight years (Umsatzsteuergesetz). Keeping them as a reproduction on an image carrier or on other data carriers is only permitted if the records remain available at all times, can be made readable without delay and are machine-evaluable throughout that period (Abgabenordnung). The match produces the trail that makes this provable.
Why an invoice on its own proves nothing
In accounts payable, three documents meet that are created in three different places. The purchase order comes from procurement and records what was ordered, at what price and on what terms. The goods receipt is created in the warehouse and records what actually arrived. The invoice comes from the supplier and names the amount to be paid. Each of these documents is incomplete on its own. Only the comparison answers the three questions that precede every payment: did we order this, did we receive it, and is the price the agreed one? Where this comparison is done by hand, it travels through the company as paper or as an attachment and pauses at every stop. What such pauses cost is worked out in detail in the article on what a single case really costs.
The starting point is well measured. A survey of 201 German mid-sized companies puts the degree of digitalisation in finance at 82 per cent, but at only 67 per cent for the processing of incoming invoices (IW Consult 2025). With formats the gap is even clearer: 26 per cent of incoming invoices arrive on paper, 55 per cent as a digital but not directly processable document, and only 19 per cent in a structured format (IW Consult 2025). Four out of five incoming invoices therefore have to be read before anything can be compared at all. How that reading step can be implemented technically, and where its limits are, is described in the article on text recognition in practice.
The price of this manual work can be quantified. Mean processing costs per incoming invoice are 15.69 euros (BME 2018). The figure comes from a 2017 data collection across four industry groups - metal, electrical and plastics manufacturing together with mechanical engineering; energy, utilities and public-law bodies; service providers; chemical, bio and pharmaceutical industry -; the source states neither a number of participants nor any reference to the Mittelstand. The same survey reports 1.29 invoices per purchase order (BME 2018) - an indication that partial deliveries, supplementary charges and freight surcharges are not the exception but the normal case the match has to handle. On the time axis the difference is similar: compared with processing a paper invoice, handling a structured invoice saves about a third of the time, and compared with a PDF document about one minute per invoice (IW Consult 2025). If all incoming invoices arrived in a directly processable e-invoicing format, extrapolation to the German Mittelstand would give a saving potential of 9.2 million working hours per month and around 3.4 billion euros in wage costs per year (IW Consult 2025). Both figures apply to that full conversion; with a 19 per cent share of structured formats it has not been reached.
What the match actually compares
What the law requires of the document
The three-way match is not purely a question of efficiency. It touches three areas of law at once, and in all three the checked document is the precondition for something else. For VAT purposes, input VAT deduction depends on the invoice: exercising it requires the business to hold an invoice issued in accordance with the statutory rules (Umsatzsteuergesetz). Under civil law, the receipt of the invoice determines when the payment period starts to run (Bürgerliches Gesetzbuch). Under tax procedure law, the document has to be kept for years; where it is kept as a reproduction on an image carrier or on other data carriers, it has to stay available and machine-evaluable (Abgabenordnung). Anyone who puts these three requirements side by side already has the checklist for the match. The basics of storage are covered in the article on GoBD-compliant document storage.
| What is checked | Where the value comes from | What a deviation triggers | Reference |
|---|---|---|---|
| Name and address of both parties | Supplier master record and invoice | Query with the supplier, correction before posting | sec. 14 (4) no. 1 (Umsatzsteuergesetz) |
| Tax number or VAT identification number | Supplier master record | Payment stays blocked until the detail is supplied | sec. 14 (4) no. 2 (Umsatzsteuergesetz) |
| Sequential invoice number | Invoice | Check against numbers already posted, suspicion of duplicate entry | sec. 14 (4) no. 4 (Umsatzsteuergesetz) |
| Quantity and customary description | Order and goods receipt | Quantity deviation, partial delivery or wrong line | sec. 14 (4) no. 5 (Umsatzsteuergesetz) |
| Date of delivery | Goods receipt posting | Invoice ahead of delivery, check of period assignment | sec. 14 (4) no. 6 (Umsatzsteuergesetz) |
| Consideration, tax rate and tax amount | Order and invoice | Price deviation or arithmetic error, price exception | sec. 14 (4) nos. 7 and 8 (Umsatzsteuergesetz) |
| Payment term and verification period | Framework agreement and order | More than 60 or 30 days only on an express agreement | sec. 271a (1) and (3) (Bürgerliches Gesetzbuch) |
| Retention of the checked document | Archive | Where stored on an image or data carrier: records not available or not machine-evaluable | sec. 147 (2) no. 2 (Abgabenordnung) |
The mandatory particulars (Umsatzsteuergesetz) are so useful for the match because almost all of them can be checked by machine. An amount without a tax rate, a missing invoice number or an issue date that falls before the goods receipt are rules a system works through in seconds. Two of the ten particulars, however, are only required in the cases the statute names: the notice of the retention obligation, and the word "Gutschrift" where the recipient issues the invoice. A rule that enforces all ten fields on every invoice creates exceptions without cause. The issuing deadline belongs in the check as well: in the cases named in the statute the supplying business is obliged to issue an invoice within six months of performing the service (Umsatzsteuergesetz). An invoice that arrives a year after delivery is therefore rarely a purely accounting matter but first of all a question for procurement.
On top of this comes the move to structured formats. For turnover between domestic businesses a transitional rule applies: for turnover carried out after 31 December 2026 and before 1 January 2028, paper or - subject to the consent of the recipient - an unstructured electronic format may still be used until 31 December 2027 if the total turnover of the issuing business in the preceding calendar year did not exceed 800,000 euros (Umsatzsteuergesetz). After that the machine-readable document is the default case - and thus the basis on which a match can work without an intermediate step. What this means for outgoing invoices is set out in the article on the e-invoicing mandate in 2027.
Three documents, three data sources
The match is only as good as the data it works on. In practice it rarely fails on the logic and often on a master record that two systems write differently. If the ERP keeps an article number with a leading zero and accounting keeps it without, no comparison takes place. If the same supplier is set up twice, the history is split across two accounts and the duplicate check finds nothing. So before rules are formulated, the master data belongs on the table; the article on getting master data in order covers this.
The second sore point is the goods receipt. A match that is meant to check the delivered quantity needs a posting that is created promptly and line by line - not a delivery note collected and entered at the end of the month. One retention rule is worth noting here: for delivery notes received that are not accounting documents, the retention period ends when the invoice is received (Abgabenordnung). That receipt is precisely the moment at which the match takes place. Anyone who does not have the delivery note available digitally by then loses the only document that evidences the delivered quantity. How the route from the loading bay to the posting can be shortened is shown in the article on streamlining warehouse processes.
- One order number per case that appears on the invoice: without it, every check starts with a search. The number belongs in the order confirmation and in the supplier agreement.
- A line-accurate goods receipt posting with a date: the date of delivery is a mandatory particular of the invoice (Umsatzsteuergesetz) and therefore a checkable field, not a matter of experience.
- One master record per supplier, with tax number or VAT identification number, bank details and payment terms - see finding and merging duplicates.
- Prices and terms as data and not as text in the framework agreement: a discount that only procurement knows about is a deviation as far as the match is concerned.
- A machine-readable invoice intake, because so far only 19 per cent of incoming invoices arrive in a structured format (IW Consult 2025).
- A marker for invoice numbers already posted per supplier, so that the second delivery of the same invoice is noticed - see preventing duplicate postings.
These six points sound like preparatory work, and that is what they are. But they are not an additional task, they are the task itself: a match that works on clean fields needs no exception rules. A match that works on unclean fields produces so many exceptions that checking by hand starts to look faster again. In our experience the success of an invoice project is decided at this point and not by the software.
Setting the tolerance band
A match that turns every deviation into an exception is unusable. Freight costs, rounding at the second decimal, weight tolerances for bulk goods and price scales that refer to the total quantity all produce differences that nobody wants to examine. The tolerance band describes which difference passes through without a human decision. It typically consists of three limits: an absolute amount, a percentage and a quantity limit. It makes sense to set all three, because each on its own errs in one direction - a percentage is too tight on a small invoice and too wide on a large one.
The limits do not come from instinct but from your own records. Two months of invoices, sorted by the size of the deviation, show the point at which the curve flattens. Below that point lies effort without return: clarifying a difference of eighty cents costs more than it brings in when processing one invoice costs 15.69 euros on average (BME 2018, four industry groups; your own figure may be higher or lower). Above it lies money worth collecting. It matters that the limit is fixed in writing and not hidden in the software; it is a commercial decision and belongs in the process documentation.
A second limit is often forgotten: direction. An invoice below the ordered price is not a deviation that costs money but one that saves money. It should still be checked, because it can point to a wrong line or a partial delivery. As a rule an asymmetric setting works well: tight upwards, wide downwards, but logged in both directions. That keeps the trail complete without increasing the number of exceptions.
Three-way match - rule set per invoice line
1 Assignment
Order number + line present? no -> exception "no reference"
Goods receipt posted? no -> exception "no goods receipt"
Invoice number already used? yes -> exception "duplicate"
2 Quantity
invoiced == delivered -> continue
invoiced < delivered -> partial invoice, keep open
invoiced > delivered -> exception "quantity"
3 Price
|invoiced - ordered| <= 1.00 EUR -> tolerance
|invoiced - ordered| <= 2 % of the value -> tolerance
otherwise -> exception "price"
4 Arithmetic check
sum of lines + freight == net amount -> continue
tax rate and tax amount consistent -> continue
otherwise -> exception "invoice"
5 Mandatory particulars (UStG sec. 14 (4))
nos. 1 to 8 present -> post
no. 9 only with a retention notice -> otherwise not applicable
no. 10 only for a self-billed invoice -> otherwise not applicable
field required in this case missing -> exception "formal defect", payment blocked
Result: post | log tolerance | exception with owner and deadlineThe rule set looks technical, but it is above all an agreement between procurement, the warehouse and accounting. Every line answers the question of who decides in case of doubt. That is why it is sensibly produced in a joint meeting and not in a configuration dialogue. How such rules can later be represented as a workflow is described in the article on digitising approval workflows.
What changes in day-to-day work
The most visible effect is not the minute saved but the changed distribution of work. Before the match, accounting deals with all invoices with equal intensity, because it does not know in advance which one is in order. After the match it only deals with those that deviate. How large the share of invoices passing straight through turns out to be depends on the individual set of records: what matters is how many invoices carry an order number and a posted goods receipt at all. That rate only becomes reliable with the two-month survey from step 1, not with an estimate made in advance; the rest is split between tolerance cases and genuine exceptions. This shift is the real gain, and it can be measured as soon as the company reports the rate month by month.
The second effect concerns waiting time. An invoice waiting for a signature is, as a rule, not waiting for a decision but for an opportunity. The match takes the detour away from these invoices: where nothing deviates, there is nothing to decide. Waiting time for the bulk of the records therefore drops to almost zero, and the early payment discount window stays intact. How the other side - your own incoming payments - can be put in order is covered in the article on automating dunning.
Agreement costs nothing
What is identical in all three documents is posted and not read. The check stays complete because it is logged, but it no longer occupies working time.
Tolerance instead of exception
Small differences pass through within a band set in advance. The band is a commercial decision with an amount, a percentage and a quantity limit, not a setting in a program.
Exceptions with a name
Every deviation gets a role, a deadline and a status. Procurement owns the price, the warehouse owns the quantity and accounting owns the formal defect.
Early payment discount stays reachable
Waiting time falls wherever there is nothing to decide. The discount window therefore stays usable for the bulk of the records without anyone monitoring dates.
Double payment is noticed
The invoice number per supplier is checked against what has already been posted. The second delivery of the same invoice creates an exception instead of a second payment.
A trail for the audit
Every decision the match makes is recorded with a timestamp and a rule. That makes it traceable why an invoice was posted - even years later (Abgabenordnung).
These six effects are connected, but they do not arrive at the same time. As a rule the duplicate check works first, because it needs no master data work. Tolerance follows once the records have been evaluated. Automatic pass-through comes last, because it presupposes a clean assignment of order and goods receipt. That order is also the sensible order of introduction.
Every exception needs an owner
Automated accounts payable rarely fails on the invoices that pass through and often on those that do not. The exception is where it is decided whether the company gains time. It needs the same four details as any other case: a type, a role, a deadline and a status. The type follows from the rule that fired. The role follows the type and not the person, so that ownership survives a holiday. The deadline follows the payment terms. The status says what is being waited for - a reply from the supplier, a subsequent posting in the warehouse or a decision in procurement.
It matters that the exception does not remove the invoice from the records. An invoice sitting in a mailbox is invisible; an invoice with the status "price clarification" can be evaluated. Only then is it possible to say at the end of the month how many exceptions of each type occurred, how long they were open and which supplier caused them. This evaluation is the feedback channel into procurement, and it is often worth more than the time saved in the invoice run itself.
Exception - four details that belong to every case
Type price | quantity | no reference | no goods receipt | formal defect | duplicate
Role price -> procurement
quantity -> warehouse
no reference -> procurement
formal defect -> accounting
duplicate -> accounting
Deadline payment term minus 5 working days
with discount: discount period minus 3 working days
Status open -> with the supplier -> internal clarification -> decided
Monthly evaluation
count per type shows which rule is set too tight
time until decided shows where the role is unstaffed
count per supplier shows where an agreement is missing
Rule: no exception without a role, no role without a deputyThe last line is the most important. Ownership without a named deputy is ownership on borrowed time, and accounts payable has the unpleasant habit of continuing precisely during the holiday season. How ownership and deadlines can be monitored permanently without anyone maintaining a list is described in the article on tracking inspection deadlines.
Deadlines, discounts and default
The check does not take place in a legal vacuum. The debtor of a monetary claim is in default at the latest if they do not pay within 30 days of the due date and receipt of an invoice or equivalent statement of payment (Bürgerliches Gesetzbuch). The receipt of the invoice is therefore the moment at which the clock visibly starts to run - regardless of whether the invoice has been checked. A match that takes two weeks uses up half of that time before anyone even decides on the payment.
Agreeing longer periods is limited too. An agreement under which performance can only be demanded after more than 60 days is only effective if it was made expressly and is not grossly unfair having regard to the interests of the creditor (Bürgerliches Gesetzbuch). The same applies to the checking time itself: an agreement under which the time for verification or acceptance is more than 30 days after receipt of the counter-performance also requires an express arrangement (Bürgerliches Gesetzbuch). So anyone planning a long checking period as a buffer is moving an operational problem into a contract that can only carry it so far.
Where the period really starts
Introducing it in six steps
Introduction does not begin with a selection but with a survey. Anyone who does not know how many invoices arrive without an order reference cannot write a rule set. The following six steps can be worked through in a mid-sized company within a few weeks, with the effort unevenly distributed: the first two steps cost time, the last four cost coordination. An overview of the approach is given in the article on when automation pays off.
Step 1: evaluate two months of incoming invoices
Every incoming invoice is given three attributes: with or without order reference, with or without a posted goods receipt, and format. After two months it is clear what share is eligible for a match at all and where the gap lies. This survey replaces every estimate.
Step 2: sort deviations by size
All differences from the same period are sorted by amount. The point at which the curve flattens is the candidate for the tolerance limit. Quantity and percentage are looked at separately as well, so that small invoices do not fall under the same rule as large ones.
Step 3: sort out master data and number ranges
Article numbers, supplier records and order numbers are reconciled between the ERP and accounting. Spellings are unified, duplicates merged, number ranges documented. Without this step the match produces exceptions that are not exceptions.
Step 4: agree the rule set in writing
Procurement, the warehouse and accounting jointly define which deviation goes where, which deadline applies and who deputises. The result is a sheet of paper, not a program dialogue. It then belongs in the process documentation, because it describes a decision that matters for the books.
Step 5: build the interface between the systems
Order, goods receipt and invoice have to meet in one system. Whether accounting pulls the data from the ERP or the other way round is a question of the system landscape - the trade-off is described in the article on interface or manual work.
Step 6: start with one group of suppliers
The first run does not cover all suppliers but the ten with the highest invoice volume and a clean order reference. After four weeks there is a reliable rate, and the rules can be adjusted before the rest follows.
Every incoming invoice is given three attributes: with or without order reference, with or without a posted goods receipt, and format. After two months it is clear what share is eligible for a match at all and where the gap lies. This survey replaces every estimate.
All differences from the same period are sorted by amount. The point at which the curve flattens is the candidate for the tolerance limit. Quantity and percentage are looked at separately as well, so that small invoices do not fall under the same rule as large ones.
Article numbers, supplier records and order numbers are reconciled between the ERP and accounting. Spellings are unified, duplicates merged, number ranges documented. Without this step the match produces exceptions that are not exceptions.
Procurement, the warehouse and accounting jointly define which deviation goes where, which deadline applies and who deputises. The result is a sheet of paper, not a program dialogue. It then belongs in the process documentation, because it describes a decision that matters for the books.
Order, goods receipt and invoice have to meet in one system. Whether accounting pulls the data from the ERP or the other way round is a question of the system landscape - the trade-off is described in the article on interface or manual work.
The first run does not cover all suppliers but the ten with the highest invoice volume and a clean order reference. After four weeks there is a reliable rate, and the rules can be adjusted before the rest follows.
After these six steps there is no finished system but a running operation with measurable figures: share of automatically posted invoices, number of exceptions per type, average waiting time until payment. These three figures are enough to decide on any further stage of expansion. Which metrics carry weight in the invoice run and which merely create activity is sorted out in the article on metrics that actually help.
The rule matters more than the software
Retaining and evidencing
- Invoices must be retained for eight years; the period begins at the end of the calendar year in which the invoice was issued (Umsatzsteuergesetz).
- Where the records are kept as a reproduction on an image carrier or on other data carriers, that is only permitted if they are available at all times throughout the period, can be made readable without delay and can be evaluated by machine (Abgabenordnung); annual financial statements, the opening balance sheet and the documents under section 147 (1) no. 4a are excluded from this.
- For delivery notes received that are not accounting documents, the retention period ends when the invoice is received (Abgabenordnung) - so the evidence of the delivered quantity has to be secured before then.
- The decision the match made belongs in the same archive as the document, with timestamp, rule and result, so that it remains traceable later why the invoice was posted.
- The storage location and the procedure are documented, because otherwise an audit fails on the evidence - see meeting retention periods digitally.
- The records are held against the stocktaking data once a year so that goods receipts and inventory agree - see the article on preparing the stocktake.
Retention is not an appendix to the match but its result. A match produces exactly the trail a later audit wants to see: which document was compared with which, which rule fired and who decided the exception. Anyone who does not store that trail has automated but evidenced nothing. Where the archive is created technically is described on the service page for document digitisation; how the systems come together for it is set out on the page about integrations.
The most expensive invoice is not the one that is wrong but the one where nobody can say whether it was checked. It costs twice: once for the check and once for checking the check.
Sources and studies
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