Late-payment interest on a Swedish debt
How to use the calculator
Enter the overdue principal and the number of days for which interest applies. The advanced settings let you change the Riksbank reference rate and the interest margin. From 1 July through 31 December 2026, Sweden's reference rate is 2.00 percent. The Interest Act baseline adds 8 percentage points, producing 10 percent a year where that rule applies.
The calculation
The tool uses simple interest: principal × annual rate × days / 365. A SEK 10,000 debt at 10 percent costs about SEK 2.74 per day and SEK 82.19 over 30 days. It does not add accrued interest back to principal, and it excludes reminder fees, debt-collection charges, and other claim items.
When does interest start?
The amount alone cannot answer that. A contractual due date may control, while the Swedish Interest Act contains separate rules where no due date was fixed in advance. The kind of claim, the date a valid demand reached the debtor, and special legislation may matter. Check the agreement and sections 3–4 of the Act before using a day count in a real claim. This calculator provides arithmetic, not legal advice.
When a period crosses a half-year
The Riksbank sets the reference rate twice each year. Statutory late interest can therefore change on 1 January or 1 July while a debt remains unpaid. Split the period at that date and calculate each part using the rate then in force. Also check whether the parties validly agreed another rate. Keep the due date, payment date, and rates with your calculation so another person can reproduce it.