# Calculating default interest: formula, current rate and a reminder template

> German default interest is 9 percentage points above the base rate when no consumer is involved, and 5 points when one is. With the base rate at 1,52 % (in force since 1 July 2026) that means 10,52 % and 6,52 % per year. In Austria, business-to-business default interest is 10,73 %.

Source: https://back-bone.io/en/blog/verzugszinsen-berechnen-mahnung-muster  
Published: 2026-08-28 · Updated: 2026-10-07  
Category: Guides

[Calculate it in 10 seconds: late-payment interest calculator](https://back-bone.io/en/tools/late-payment-interest-calculator)

## The current default-interest rate

The statute names no fixed percentage. It names a margin on top of the **base rate** under § 247 BGB, which the Bundesbank publishes and resets twice a year, on 1 January and 1 July. Copying a rate from an older article is therefore almost always wrong.

| Case | Legal basis | Rate p.a. |
| --- | --- | --- |
| Germany, a consumer is involved | § 288 Abs. 1 BGB (5 %-Punkte) | 6,52 % |
| Germany, business to business | § 288 Abs. 2 BGB (9 %-Punkte) | 10,52 % |
| Austria, business to business | § 456 UGB (9,2 %-Punkte) | 10,73 % |
| Austria, otherwise | § 1000 ABGB | 4,00 % |

The two base rates are not identical: Germany is at 1,52 %, Austria at 1,53 % (both as of 1 July 2026). They are calculated differently, so never apply the German figure to an Austrian claim. The OeNB raised its base rate to 2,03 % on 16 September 2026, but default interest uses the rate in force on the first calendar day of the half-year (§ 456 UGB), so it stays at 1,53 %, and 10,73 %, until 31 December 2026. Sources: Deutsche Bundesbank, OeNB and WKO.

## The formula, worked through

Interest = amount due × rate × days in default ÷ 365.

Example: a B2B invoice for **2.400 €**, **30 days** in default, at 10,52 %: 2.400 € × 10,52 % × 30 ÷ 365 = **20,75 €**, plus the 40 € flat fee. In Austria the same formula applies, with 10,73 %.

Count from the day after default begins up to and including the day of payment; if the period crosses 1 January or 1 July, split it there. [Calculate it in 10 seconds: late-payment interest calculator](https://back-bone.io/en/tools/late-payment-interest-calculator)

## When you may start charging

Interest does not run from the invoice date but from the moment of default. Three routes get you there:

1. You send a reminder after the due date. Default begins when it arrives — one is enough; the widely believed "three reminders" rule is not in the statute.
2. You agreed a fixed payment date ("payable by 15 September"). Default then starts when that date passes, with no reminder needed.
3. Default begins automatically at the latest 30 days after the due date and receipt of the invoice (§ 286 Abs. 3 BGB). Against consumers only if you said so on the invoice itself.

In Austria no reminder is needed: a business client is in default once the money has not reached your account by the payment date (§ 907a ABGB).

## Templates to copy

Stage one stays friendly and mentions no interest — most payments arrive here. Stage two puts a number on the interest and the flat fee. Replace the bracketed placeholders.

**Payment reminder (stage 1)**

```text
Betreff: Zahlungserinnerung zur Rechnung [Rechnungsnummer]

Hallo,

unsere Rechnung [Rechnungsnummer] vom [Rechnungsdatum] über 2.400 € war am [Fälligkeitsdatum] zur Zahlung fällig. Ein Zahlungseingang ist bislang nicht zu verzeichnen.

Wir bitten dich, den offenen Betrag bis zum [neues Datum, i. d. R. 7–14 Tage] auf folgendes Konto zu überweisen:

[Kontoinhaber]
IBAN: [IBAN]
BIC: [BIC]
Verwendungszweck: [Rechnungsnummer]

Sollte sich deine Zahlung mit diesem Schreiben überschnitten haben, betrachte es bitte als gegenstandslos.

Viele Grüße
[Name]
```

**Reminder with interest (stage 2)**

```text
Betreff: Mahnung zur Rechnung [Rechnungsnummer]

Hallo,

trotz unserer Zahlungserinnerung vom [Datum] ist die Rechnung [Rechnungsnummer] vom [Rechnungsdatum] über 2.400 € weiterhin offen. Du befindest dich seit dem [Datum des Verzugseintritts] in Zahlungsverzug.

Wir stellen dir daher in Rechnung:

  Hauptforderung:              2.400 €
  Verzugszinsen (10,52 % p. a.,
  30 Tage):                     20,75 €
  Pauschale nach § 288 Abs. 5 BGB:  40 €
  ------------------------------------------------
  Gesamtbetrag:                2.460,75 €

Wir bitten um Überweisung des Gesamtbetrags bis zum [Datum] auf das unten genannte Konto.

Viele Grüße
[Name]
```

For clients abroad, the same stages in English are in [payment reminders in English](https://back-bone.io/en/blog/mahnung-auf-englisch). The full process, from first contact to a court order, is in the reminder guide.

## Three mistakes that cost money

1. Using the wrong margin. The 9 points apply only when NO consumer is involved on either side. As soon as a private client is, it drops to 5 — claim too much and you have to walk it back.
2. Using a stale base rate. It changes on 1 January and 1 July; an article from a year ago will name a different figure.
3. Charging the 40-euro flat fee to a consumer. It exists for business dealings only.

### How Backbone handles this

Backbone spots overdue invoices from their due date and sends the reminder and the dunning notice automatically, on the schedule you set once — in your wording and your layout.

The AI assistant also answers the question behind all of this — "who still owes me money?" — with the amounts and how long they have been outstanding.

> I am a designer and developer, and for years I made my own invoices by hand because no tool produced one I actually wanted to send. Along the way I made just about every mistake there is — mixed-up numbers, wrong tax rates, misunderstood reverse charge.
>
> That is exactly why I write these articles and build Backbone: rules like this belong in the software, not in your memory.

Last updated 7 October 2026. Base rates verified on 7 October 2026 against Deutsche Bundesbank and OeNB, § 286 BGB on gesetze-im-internet.de, § 456 UGB on RIS.

## Frequently asked questions

### What is the current German default-interest rate?

The base rate under § 247 BGB has been 1,52 % since 1 July 2026. That makes 10,52 % per year when no consumer is involved (§ 288 Abs. 2 BGB) and 6,52 % when one is (§ 288 Abs. 1 BGB). In Austria, business-to-business default interest is 10,73 % (§ 456 UGB).

### How do I calculate default interest for a period?

Outstanding amount × rate × days in default ÷ 365. Example: 2.400 € at 10,52 % for 30 days comes to 20,75 €. Count from the day after default begins until the day of payment.

### When may I start charging default interest?

Once the debtor is in default. That happens when you send a reminder after the due date — or automatically at the latest 30 days after the due date and receipt of the invoice (§ 286 Abs. 3 BGB). Against consumers, the automatic 30-day rule only applies if you pointed it out on the invoice itself. An agreed fixed payment date also triggers default without any reminder.

### What is the 40-euro flat fee?

When a business is in default you may claim a flat 40 € on top of the interest (§ 288 Abs. 5 BGB). It applies in business dealings only — never against consumers — and is offset against any legal-costs claim you make later. Austria has an identical flat fee for collection costs.

### Reminder or "Mahnung" — what is the difference?

Legally nothing: both count as a reminder under § 286 BGB once they demand payment after the due date. The difference is tone only. Nor is there any duty to send three reminders — a single one is enough to trigger default.