German 30/360

API value: thirty_e_360_de

Also known as: 30E/360 German, deutsche Zinsmethode, kaufmännische Zinsmethode, 30/360 deutsch

German 30/360 treats every month as exactly 30 days and every year as 360 days, without exception. It is what German banks, Sparkassen and Volksbanken book on almost all loans, and it is why German repayment plans (Tilgungspläne) show the same interest share in February as in March.

Rules

The formulas use these symbols:

Step 1: adjust the days. Before counting, both days are adjusted:

• If $D_1$ is the 31st or the last day of February, it becomes 30.
• If $D_2$ is the 31st or the last day of February, it becomes 30. This also applies on the maturity date.

Step 2: count the interest days.

Formula:

$$d = 360 \cdot (Y_2 - Y_1) + 30 \cdot (M_2 - M_1) + (D_2 - D_1)$$

With the terms:

$$\text{Days} = 360 \cdot (\text{End year} - \text{Start year}) + 30 \cdot (\text{End month} - \text{Start month}) + (\text{End day} - \text{Start day})$$

With the example numbers: period from 31 January 2026 to 28 February 2026. $D_1 = 31$ becomes 30. $D_2 = 28$ is the last day of February and also becomes 30.

$$d = 360 \cdot (2026 - 2026) + 30 \cdot (2 - 1) + (30 - 30) = 0 + 30 + 0 = 30$$

Step 3: calculate the interest.

Formula:

$$I = B \cdot r \cdot \frac{d}{360}$$

With the terms:

$$\text{Interest} = \text{Balance} \cdot \text{Rate} \cdot \frac{\text{Days}}{360}$$

With the example numbers: 100,000 EUR at 4.00 % for the 30 days above.

$$I = 100{,}000 \cdot 0.04 \cdot \frac{30}{360} = 333.33$$

What this means in practice

• Every full month accrues exactly 1/12 of the annual interest.
• A full year always accrues exactly the nominal rate.
• Broken periods are counted as if each month had 30 days. A period from 15 February to 28 February 2026 counts 15 days, not 13.
• Only the last day of February is adjusted. In a leap year, 28 February is an ordinary day: a period from 28 February to 31 March 2028 counts 32 days.

Example

100,000 EUR at 4.00 % p.a., balance unchanged.

How to recognise it in a contract

• "Die Zinsen werden nach der deutschen kaufmännischen Zinsmethode berechnet."
• "Monat zu 30 Tagen, Jahr zu 360 Tagen" or "30/360" from a German lender.
• The bank's Tilgungsplan shows identical interest in February and in 30- and 31-day months while the balance is unchanged.

Related

• Guides overview
• 30E/360 (Eurobond)
• 30/360 US (Bond Basis)