Hi all,
I have a question regarding interest calculation in Dynamics 365 Finance and would like to know whether anyone has already dealt with this requirement.
For a loan, we need to use the commercial 30/360 day-count convention in germany and switzerland.
In standard D365 Finance, the Day method with an interval of 1 day appears to use a 360-day annual basis as well, but the number of interest days is determined differently.
Technically, with Day + Percentage, D365 calculates:
Amount × Monthly interest rate × Actual interest days / 30
For an annual interest rate of 1%, the monthly interest rate is configured as:
1% / 12 = 0.083333%
This results mathematically in:
Amount × 1% × Actual interest days / 360
So effectively, this corresponds to an Actual/360 calculation.
The difference compared with the required 30/360 method is the way the interest days are counted:
- D365 Day uses the actual calendar days.
- Under 30/360, each month is treated as having 30 days, and the 31st day is adjusted accordingly.
A few examples illustrate the difference:
| Period | D365 Day / Actual days | Commercial 30/360 |
|---|
| 04 Mar – 31 Mar | 27 days | 26 days |
| 18 Mar – 31 Mar | 13 days | 12 days |
| 11 Feb – 31 Mar | 49 days | 49 days |
| 15 Jan – 31 Mar | 76 days | 75 days |
| 04 Feb – 28 Feb | 24 days | 24 days |
| 18 Feb – 28 Feb | 10 days | 10 days |
| 26 Jan – 28 Feb | 33 days | 32 days |
The difference becomes particularly visible when moving from January to February, because D365 uses the actual number of calendar days, while 30/360 uses a standardized 30-day month.
As far as I can see, the other standard calculation methods do not solve this requirement either:
- Month: Monthly interest rate × number of monthly intervals
- Calendar day: Monthly interest rate prorated based on the actual number of days in the month, e.g. 1/28, 1/29, 1/30 or 1/31
- Day365: Annual interest rate × actual days / 365
Has anyone implemented a true 30/360 day-count convention in Dynamics 365 Finance?
If so, how did you solve it?
My current assumption is that a small customization would be required to adjust the calculation of the interest days, while the existing interest formula could largely remain unchanged.
I would appreciate any experience or recommendations without development.
