Invoice overdue simple interest and payments calculator

Define when an invoice first becomes overdue

The due date itself accrues no interest in this model. The following date is the first overdue day, and the as-of date is included. These endpoints matter when comparing a hand calculation with a ledger that uses another convention.

Payments are applied before interest on their own dates. A partial payment therefore reduces that day’s interest-bearing principal. The event table shows the principal remaining and cumulative interest at payment dates and at the calculation endpoints.

The Credit card daily interest ledger calculator distinguishes simple accrual from daily capitalization. This invoice ledger deliberately keeps accrued interest separate from principal and makes no assumption about card policies.

Principal-only payments keep the model transparent

Every payment entered here reduces principal. Accrued interest remains separate and is never capitalized. If a contract applies receipts to fees or interest first, its balance schedule requires that different allocation rule.

A payment larger than the remaining principal is rejected. The tool does not silently turn it into a negative principal balance or assume that excess pays accrued interest, because either action would change the stated model.

A numerical rate does not create a legal right

This is contractual arithmetic from an annual rate you supply. It does not decide whether interest is enforceable, whether a statutory rate applies or whether another notice is required. Verify the underlying agreement and the relevant jurisdiction separately.

Use the worked example as a timing check. Moving a principal payment one day earlier should reduce interest by one day’s rate on the payment amount, provided the other endpoints stay fixed. That gives a useful independent check on the ledger.

Work through the example

At 36.5 percent actual/365, 10,000 accrues 10 per overdue day. A 5,000 principal payment before January 6 interest gives four days at 10 and six days at 5 through January 11, totaling 70.

Use the worked table to trace where each input enters. Then change one assumption and calculate again, leaving the others fixed. A comparison is easier to interpret when the change has one identifiable cause rather than a different set of measurements, dates and rates all at once.

What this model does not establish

Actual/365 simple interest only, up to 3,660 overdue days. No legal entitlement, statutory rate lookup, penalty fees, compounding, credit balance or payment-to-interest allocation. Confirm contractual and legal requirements.

Keep the input assumptions with any exported result. Illustrative values do not become observations merely because the output is precise. For a real purchase, financial reconciliation or technical decision, check the underlying records and applicable requirements before treating this scenario as a final answer.