Duplicate payments
Same vendor, same amount, close in time — plus the same reference whatever the date.
- Runs
- In this tab
- Data sent
- None
- Rounding
- Once, at the end
- Also in
- The Chrome extension
Duplicate payments, worked
Showing a worked example — type over it
Result
How the duplicate payments works.
Duplicate finder: The same reference whatever the date, same vendor + amount within N days (14 by default — under a month, so rent is not flagged), and same-amount/different-vendor.
Quoted from the toolbelt spec, the document this tool was built against.
Where these numbers come from.
Negatives are parenthesised because that is what a statement does. The rest is four promises.
Minor units, never floats
Amounts are integers in the currency's smallest unit, end to end. A float never touches a cent.
Rounded once
Rounded once, at the end — never per operand, which is how a split stops summing to the whole.
Unit tested
The arithmetic lives in one unit-tested module, shared without reimplementation with the extension.
No network
There is no request to make. What you type stays in this tab and is gone when you close it.
More in reconciliation & investigation
- Difference diagnoserOut by 8,100? That is divisible by 9 — a transposition. This says which error fits the gap.
- Which invoices make this deposit?A deposit against forty open items. Exact subset-sum over minor units — no floating point.
- Two-list matcherBank against ledger: exact, then reference, then a date window, then one-to-many — and what is left on both sides.
- Benford & round numbersTwo cheap tests over a pasted column. Neither proves anything; both tell you where to look.
Read it in context
- Founder guide · 6 minW-9s and backup withholding: a vendor onboarding guideWhen to ask for a W-9, how IRS TIN matching works, and what happens when a vendor won’t give you one: 24% backup withholding, owed by you.
- Founder guide · 7 minBalance sheet explained for startupsAssets equal liabilities plus equity. What each startup line means, from deferred revenue to the SAFE and the accumulated deficit, and why it must balance.
- Founder guide · 5 minCash flow statement explained: why profit isn’t cashHow the cash flow statement starts at net income, adds back non-cash costs and working capital, splits three activities and ties to the balance sheet.
The same number, elsewhere.
A calculator answers the question once. These carry the answer into a product, name what it computed, and argue the method.
- ComponentDuplicateBillAlertBlocking. Duplicate payment is the most common AP loss.
- ComponentPaymentRunBuilderShows the cash balance remaining after the run.
- ComponentApprovalInboxMobile-first, document inline.
- TermBillA claim against us
- TermPayment runA batch of payments released together
- TermSegregation of dutiesSplitting authorization, recording, custody of assets and reconciliation across different people, so no one person can both commit and conceal an error or fraud — at minimum, preparer ≠ approver
- TermAccounts payableWhat we owe vendors for bills already received
- DocProcure to pay (AP)The complete payables stack: requisition → PO → receipt → bill → approval → payment → reconciliation. AP is where fraud happens and where controls matter most. The design consequence: Every AP screen is a control surface. Approval, segregation of duties, and duplicate detection are not features bolt
- DocControls & auditAccounting software is not a database with forms on top. It is a system of controls, and the UI is where most of those controls are actually enforced.
- EntryJournal entry for accounts payableWhen an approved vendor bill is entered, debit the expense or asset it bought and credit Accounts payable. When it is paid, debit Accounts payable and credit Cash.
- DocCurrency decimal placesHow many decimals each ISO 4217 code is stored at — JPY 0, USD 2, KWD 3.