Anyone who pays a money debt late owes default interest on top of the debt, from the day it fell due until the day it is paid. The statutory rate is set twice a year by the Central Bank of Montenegro as the European Central Bank's main refinancing rate plus eight percentage points. From 1 July to 31 December 2026 the rate is 10.40% a year, and in the first half of the year it was 10.15%. Interest is calculated as simple interest, without adding interest to the principal, so a debt of 1,000 euros that is 90 days late in the second half of 2026 earns 25.64 euros of interest. For debt to the Tax Administration, a separate rate of 5.4% a year has applied since 18 July 2026, instead of the former 0.03% a day.
This guide explains what the rate is, when it applies, how to calculate the interest yourself, what applies to tax debt and what the rates have been since 2023.
What is the default interest rate in 2026?
| Period | Default interest rate |
| 1 July to 31 December 2026 | 10.40% a year |
| 1 January to 30 June 2026 | 10.15% a year |
| debt to the Tax Administration, 18 July to 31 December 2026 | 5.4% a year |
- The rate is set for half-years, from 1 January to 30 June and from 1 July to 31 December, and is calculated on an annual basis.
- The base rate is the rate the European Central Bank applies to its main refinancing operations on the first day of the half-year, and the law adds eight percentage points.
- The Central Bank publishes the rate on its website on the first working day of the half-year and in the Official Gazette.
When is default interest payable?
- A debtor who pays late owes default interest on the amount of the debt until the day of payment, for example on rent, the return of a deposit or earnest money, a private loan or an unpaid invoice.
- The statutory rate applies when no default interest rate has been agreed in the contract, so check the contract first.
- The law does not apply to late payments for which another law sets a different rate, such as tax debt.
- Interest runs from the day the debt fell due, that is, from the day the debtor fell behind with payment.
How is default interest calculated?
- Default interest is calculated as simple interest on the principal that has fallen due, without adding interest to the principal at the end of the calculation period.
- The formula is principal times rate times number of days, divided by 36,500, and in a leap year by 36,600.
- Example: for a debt of 1,000 euros that is 90 days late in the second half of 2026, interest is 1,000 × 10.40 × 90 / 36,500 = 25.64 euros.
- If the delay runs across two half-years, you calculate the days of each half-year at the rate for that half-year.
- Calendar days are counted, including weekends and public holidays.
What applies to debt to the Tax Administration?
- Amendments to the Tax Administration Act from 18 July 2026 replaced the old rate of 0.03% a day with a new rate calculated as the European Central Bank rate plus three percentage points.
- The Tax Administration set the rate at 5.4% a year for the period from 18 July to 31 December 2026.
- Interest is payable from the day after the due date, on tax that was not paid or was underpaid.
- For a tax debt of 1,000 euros that is 90 days late, that is 13.32 euros, while under the old daily rate it was 27 euros.
- If you paid more tax than you owed, you are entitled to interest at the same rate, calculated within 30 days of your refund request.
What have the rates been since 2023?
| Half-year | Rate |
| second half of 2026 | 10.40% |
| first half of 2026 | 10.15% |
| second half of 2025 | 10.15% |
| first half of 2025 | 11.15% |
| second half of 2024 | 12.25% |
| first half of 2024 | 12.50% |
| second half of 2023 | 12.00% |
| first half of 2023 | 10.50% |
- For an older debt, you calculate interest at the rate of each half-year in which the debt was late, not at today's rate.
- Late payments between businesses, where contracts and payment deadlines follow separate rules, are covered by RoNa Legal.
When earnest money is returned with interest is explained in our guide to earnest money and preliminary contracts, and the return of a rental deposit in our guide to ending a lease. When a debt becomes time-barred is covered in our guide to the limitation period for debts, and tax deadlines in our guide to the annual income tax return.
Frequently asked questions
What is the default interest rate in Montenegro in 2026? From 1 July to 31 December 2026 it is 10.40% a year, and from 1 January to 30 June 2026 it was 10.15%.
How is default interest calculated? Multiply the principal by the rate and the number of days late and divide by 36,500, or by 36,600 in a leap year, without adding interest to the principal.
Who sets the default interest rate? The Central Bank of Montenegro, twice a year, as the European Central Bank's main refinancing rate plus eight percentage points.
Can a different rate be agreed? Yes, the statutory rate applies when no default interest rate has been set in the contract.
What is the interest on tax debt? From 18 July to 31 December 2026 it is 5.4% a year; before that it was 0.03% a day.
Is interest charged on interest? No, default interest is simple interest charged only on the principal and is not added to it.
Sources
The rate, how it is set and how it is calculated are governed by the Act on the Default Interest Rate (Official Gazette 83/2009 and 75/2018, Articles 1 to 7), and the rate for the second half of 2026 by the Central Bank decision (Official Gazette 95/2026). Interest on tax debt is governed by the amendments to the Tax Administration Act (Official Gazette 104/2026, Articles 20 and 21) and the Tax Administration decision (Official Gazette 111/2026). The rates from 2023 to 2025 come from Central Bank decisions published on its website. The information was checked on 28 September 2026. Fijaka is a classifieds platform; this text is not legal advice.