Guides
Practical guides to how LoanMonitor calculates loans, starting with the day count conventions it supports.
These guides explain how LoanMonitor calculates your loans and how to set them up so the schedule matches your bank's statements to the cent.
Day count conventions
A day count convention decides how many interest days a period accrues and how many days a year has. The same loan at the same rate produces different interest amounts depending on the convention, so it must match your loan agreement. LoanMonitor applies it to every interest calculation: regular installments, broken first and last periods, disbursement tranches, extra repayments and rate fixings.
German banks almost always book German 30/360. If your contract says "30/360" and the lender is a German bank, start there.
German 30/360
Every month is 30 days, February and maturity included. The standard for German bank loans.
30E/360 (Eurobond)
The 31st becomes the 30th; February stays as it is.
30/360 US (Bond Basis)
The 31st only becomes the 30th if the period started on the 30th or 31st.
ACT/360
Actual calendar days over a 360-day year. The money-market standard for EURIBOR and €STR.
ACT/365
Actual calendar days over a fixed 365-day year.
At a glance
| Convention | API value | Days in period | Days in year |
|---|---|---|---|
| German 30/360 | thirty_e_360_de | 30 per month, always | 360 |
| 30E/360 (Eurobond) | thirty_e_360 | 31st → 30th, February unadjusted | 360 |
| 30/360 US (Bond Basis) | thirty_360 | 31st → 30th only if start is 30th/31st | 360 |
| ACT/360 | act_360 | actual calendar days | 360 |
| ACT/365 | act_365 | actual calendar days | 365 |
Side-by-side example
100,000 EUR at 4.00 % p.a., monthly periods on the last day of each month, balance unchanged.
| Period | German 30/360 | 30E/360 | 30/360 US | ACT/360 | ACT/365 |
|---|---|---|---|---|---|
| 31 Jan → 28 Feb 2026 | 333.33 | 311.11 | 311.11 | 311.11 | 306.85 |
| 28 Feb → 31 Mar 2026 | 333.33 | 355.56 | 366.67 | 344.44 | 339.73 |
| 31 Mar → 30 Apr 2026 | 333.33 | 333.33 | 333.33 | 333.33 | 328.77 |
| 12 periods, 31 Jan 2026 → 31 Jan 2027 | 4,000.00 | 4,000.00 | 4,011.11 | 4,055.56 | 4,000.00 |
Choosing a convention
Read the contract. Look for Zinsberechnungsmethode, Zinstagezählung, day count fraction, or phrases like "30/360", "act/360", "Monate zu 30 Tagen, Jahr zu 360 Tagen".
Match it to the API value using the table above. German bank plus "30/360" means German 30/360.
Reconcile. Preview the plan and compare the first interest amount with the bank's Tilgungsplan or first statement. A difference of a few euros in February or around a 31st means the convention is wrong.
Changing the day count convention on an existing loan recalculates the whole schedule. Rate fixings, disbursements and extra repayments are kept and re-applied on the new basis.