Payment disputes often start with the calendar, not the amount. One person counts from the invoice date, another from the signed acceptance act, and someone else includes the starting day without checking the contract wording.
Qsen’s date difference calculator helps you count the interval before sending a payment reminder, preparing an overdue report, or checking whether a deadline has passed.
Identify the trigger date
Do not count anything until you know which event starts the deadline. The contract may refer to the invoice date, delivery date, signed act, receipt of documents, or another event.
If the deadline depends on document receipt, keep the proof: email timestamp, electronic document system record, or incoming registration number. A calculation is only useful when the starting point is clear.
Calendar days and business days are not the same
Calendar days run continuously, including weekends and holidays. Business days require a separate working calendar. If the contract does not say which type applies, do not guess. Check the wording before using the result in a formal letter.
The date difference calculator is ideal for calendar intervals and quick checks. For business-day clauses, use it as a starting view and then remove non-working days according to the relevant calendar.
Example: overdue invoice
Suppose the acceptance act was signed on May 12, and payment is due within 7 calendar days. If the count starts on the next day, the due date is May 19. If payment arrives on May 23, the overdue period is 4 days: May 20, 21, 22, and 23.
Before sending a reminder, write down three lines: trigger event, due date, and actual payment date or current calculation date. This makes the logic easy to check later.
Common mistakes
The first mistake is counting from the invoice when the contract refers to the act. The second is including the trigger date without support. The third is mixing calendar and business days. The fourth is counting until today even though partial or full payment arrived earlier.
For material amounts, keep the calculation and the contract clause together. It saves time if the client asks how the number was reached.
Quick checklist
- the contract clause has been found;
- the trigger date is clear;
- calendar or business days are identified;
- the due date is written separately;
- payment date and calculation date are not mixed;
- the final overdue day count is checked twice.
FAQ
Should the signing day be counted?
It depends on the clause and applicable rules. Many calculations start on the following day, but the contract wording should decide.
What if the payment was made in parts?
Count each unpaid part separately or use the full settlement date if the contract treats payment as complete only after the full amount is received.
Can I use the number in a formal demand letter?
Yes, as the arithmetic part. The legal wording and penalties should still match the contract.