No default, no default interest
The most common source of error with default interest is not the percentage arithmetic but the start date. Many creditors use the invoice date or the due date. Both are usually too early. Interest under § 288 BGB is only owed from the moment the debtor is in default. When that happens is governed by § 286 BGB. This article shows the three routes into default with concrete dates.
Route 1: The reminder
Under § 286(1) BGB the debtor falls into default through a reminder sent after the due date. A reminder is any clear demand to pay now. The word “reminder” does not have to appear; even a friendly payment notice can suffice if it clearly demands payment. Setting a deadline is not required.
Two points are decisive:
- The reminder must come after the due date. A reminder sent together with the invoice before the claim is due does not trigger default.
- Receipt is what counts. Default occurs when the reminder reaches the debtor, not when it is sent. If you may have to prove receipt later, a traceable delivery method helps.
Example: the reminder is received on 10 Mar 2026. The debtor is in default from that day. Interest is widely calculated from the following day, here from 11 Mar 2026 (§ 187(1) BGB by analogy). In the calculator you enter 11 Mar 2026 as the start of default.
Filing a lawsuit and serving a court payment order in the dunning procedure have the same effect as a reminder.
Route 2: A payment deadline fixed by the calendar
No reminder is needed if a time for payment is fixed by the calendar (§ 286(2) no. 1 BGB). That is the case with wording such as “payable by 31 March 2026” or “payment on the 15th of the month”. The debtor then knows exactly when to pay.
Example: the invoice says “payable by 31 Mar 2026”. If the debtor does not pay, they are in default from 1 Apr 2026. Interest runs from 1 Apr 2026.
It is similar if payment is preceded by an event and the period can be calculated by the calendar from that event (§ 286(2) no. 2 BGB), e.g. “payable 14 days after delivery”. Whether a clause meets these requirements is not always clear in individual cases. If you want to be safe, put a fixed date on the invoice.
Further cases in which a reminder is not needed: the debtor seriously and finally refuses to pay (no. 3), or special reasons justify immediate default (no. 4).
Route 3: The 30-day rule
For payment claims there is a fallback rule: the debtor is in default at the latest if they do not pay within 30 days after the due date and receipt of an invoice or equivalent statement of payment (§ 286(3) BGB).
How to count the period: the day of receipt is not counted (§ 187(1) BGB), and the period ends when the 30th day expires (§ 188(1) BGB). Default exists from day 31.
Example: the invoice, already due, is received on 2 Mar 2026. The period runs from 3 Mar until the end of 1 Apr 2026. From 2 Apr 2026 the debtor is in default. If they pay an invoice of €800 on 30 Jun 2026, that is 89 interest days. For a consumer whose invoice contained the notice, this gives 800 · 6.27 · 89 / 36,500 = €12.23.
In the late payment interest calculator choose “Due date & receipt of invoice” and enter the date of receipt. The calculator automatically sets the start of default to day 31.
If the time of receipt is uncertain, a debtor who is not a consumer is in default at the latest 30 days after the due date and receipt of the goods or services.
Special case: consumers
Towards consumers, the 30-day rule only applies if the invoice specifically pointed out this consequence. Possible wording: “Please note: you will be in default at the latest 30 days after the due date and receipt of this invoice if you do not pay.” Without that notice, private customers need a reminder or a payment deadline with a fixed date.
When the debtor is not responsible
Under § 286(4) BGB the debtor is not in default as long as payment is not made because of a circumstance they are not responsible for. With money debts this rarely matters, because insolvency is no excuse. It can be different, for example, if the invoice was incorrect or the work is defective and the debtor therefore rightly withholds payment.
Checklist
- Is the claim due?
- Is there a fixed payment date? Then default from the following day.
- If not: when was the reminder received? Then interest from the following day.
- Without a reminder: when did the due date and receipt of the invoice occur? Then default from day 31, for consumers only with the notice.
- The earliest of these dates applies.
What happens next is shown in the guide to late payment interest. This article is not legal advice.