How It Works
Select the start date and the end date of the calculation period, enter the principal amount on which interest accrues, choose the capitalization method, and press the Calculate button. The results will appear in the summary at the top and in the two detailed tables.
Civil Year and Day Count
The calculation always uses the civil year of 365 days, in line with established practice for Italian Legal Interest. In the past, a Commercial Year also existed, consisting of 12 months of 30 days each (360 days total). This system was used to simplify calculations but has fallen out of use with modern software. Leap years do not affect the calculation basis. The formula applied for each period is:
Interest = Principal × Rate% ÷ 100 ÷ 365 × Days
As a rule, the first day of the period is excluded from the count (dies a quo non computatur in termino), in accordance with Art. 2963 of the Civil Code. The "Include the first day" checkbox allows you to override this rule when required by a contract or title.
Legal Interest Rates
The rates are those set annually by Decree of the Ministry of Economy and Finance pursuant to Art. 1284 of the Civil Code. They are stored in the calculator from 1 January 1970 to the current year (official data).
When the calculation period spans multiple years with different rates, the principal is automatically divided into the corresponding sub-periods, each calculated at the rate in force at the time.
Legal Framework
Legal Interest is governed by Article 1284 of the Civil Code, which states the following after the amendment introduced by Article 2 of Law No. 662 of 23 December 1996: "The rate of Legal Interest is set at 5 percent per year. The Minister of the Treasury, by decree published in the Official Gazette of the Italian Republic no later than 15 December of the year preceding the one to which the rate refers, may modify it annually on the basis of the average annual gross yield of government securities with a maturity not exceeding twelve months and taking into account the inflation rate recorded during the year. If no new rate is set by 15 December, the existing rate remains in force for the following year." Naturally, over the years, the Legal Interest Rate has changed in line with inflation trends.
Rules on Time Limits
This calculator follows the provisions of Art. 155 of the Code of Civil Procedure: "in calculating time limits in days or hours, the initial day or hour is excluded," applying the Roman law principle "dies a quo non computatur in termino, dies ad quem computatur." Furthermore, under the same article, "if the deadline falls on a public holiday, it is automatically extended to the next working day," and "for time limits expressed in months or years, the common calendar applies." In summary, the initial day of a term is excluded, while the final day is included. Finally, Legal Interest must be distinguished from Monetary Revaluation, which is the mechanism used to compensate for inflation.
The Two Breakdown Tables
Breakdown by Current Rate shows the calculation without capitalizing interest: for each sub-period, interest is always computed on the original principal, without revaluation. It is useful as a basic reference (it shows Legal Interest calculated according to the regulation) and for making comparisons.
Breakdown by Capitalization shows the calculation under the selected regime (no capitalization, annual, semi-annual, etc.): at the end of each period, accrued interest is added to the principal. The total in this table always matches the summary displayed at the top.
Capitalization
When setting capitalization to every month (monthly), or every 2 (bimonthly), 3 (quarterly), 4 (four-monthly), 6 (semi-annual), or 12 months (annual), the accrual periods start on fixed dates: the first day of each month; for bimonthly capitalization: 1 January, 1 March, 1 May, 1 July, 1 September, 1 November; for quarterly: 1 January, 1 April, 1 July, 1 October; for four-monthly: 1 January, 1 May, 1 September; for semi-annual: 1 January, 1 July; for annual: 1 January.
Rounding
The interest for each period is rounded to the nearest cent before being added to the total. This choice—consistent with accounting and banking practice—may produce differences of one or two cents compared to a calculation performed on the total without intermediate rounding. Such differences are normal and do not constitute an error.
Exporting
The Copy button copies the summary and the active table as text to the clipboard. Export HTML downloads a standalone web page containing all data, which can be saved or printed. Export PDF generates an A4 document with both tables. Print opens the browser’s print dialog.