Late-payment interest calculator

Late-payment interest is calculated as a percentage of the amount due, pro rata to the number of days overdue. Swiss commercial practice uses the 360-day year:

For example, on an invoice of CHF 5,000 paid 60 days late at the 5% legal rate: 5,000 × 0.05 × 60 ÷ 360 = CHF 41.67 in interest. The total due then comes to CHF 5,041.67.

Interest is calculated only on the principal, never on interest already accrued: Swiss law prohibits compound interest (art. 105 para. 3 CO).

In the absence of an agreement between the parties, the late-payment interest rate is set at 5% per year by article 104 of the Code of Obligations (CO). This rate applies automatically, without the creditor having to prove any damage.

A higher rate can be agreed by contract or in the general terms, in which case it replaces the legal rate. In commercial matters, if the bank discount rate exceeds 5%, the creditor may claim that higher rate.

When a due date has been agreed, interest runs from the day after that date. Simply passing the due date is enough to put the debtor in default.

If no date has been set, a formal notice is required: a reminder that clearly demands payment. Interest then starts to run upon receipt of that reminder. This calculator helps you quantify the interest, but it does not replace personalised legal advice.