Why is my instalment different from the one in the calendar?

The law sets the 3% rate, the start date of 1 August 2026 and equal instalments, but does not say how days are counted or how figures are rounded. The calendar uses simple interest per period on the outstanding balance and equal instalments; the collection agency may count differently. The gap is a few euros per instalment, but the amount in the statement always prevails.

How is the last useful day worked out when there is a public holiday?

The due date moves to the next working day, then the five-day tolerance is added, and if the fifth day is a Saturday, Sunday or national public holiday it moves to the next working day. That count takes 15 September 2024 to 23 September 2024 in the collection agency’s practice. The calendar includes national holidays, Easter Monday included, but not local patron-saint days.

Does the site keep the figures I type to work out instalments?

No. Every calculation runs in the browser with the page’s own code: amounts, instalments and payment status are sent to no server. The calendar file is created on your device. If you use the share link, your choices go into the page address and only the people you send it to can see them.

Method: how instalments, due dates and lapse are worked out

The tools apply legal texts: Law 199 of 2025 (paragraphs 82 to 110), article 10-quinquies of Decree-Law 38 of 2026 as amended by Law 113 of 2026, Law 197 of 2022 (paragraphs 222 to 252), article 3-bis of Decree-Law 202 of 2024 and Presidential Decree 602 of 1973, reread on 26 October 2026, with the public FAQs of Agenzia delle entrate-Riscossione for practice. Every date, rate and threshold comes from src/data/params-2026.json; no page types a figure by hand.

The calendars

Instalment dates are copied from the texts: 54 instalments for the quinquies from 31 July 2026 to 31 May 2035, 54 for the local-authority quinquies from 31 March 2027 to 31 January 2036, 18 for the quater up to 30 November 2027, 10 for the readmission up to 30 November 2027. Anyone who chose fewer instalments follows the first dates of the calendar. The 2024 quater extensions (first three instalments to 15 March 2024, fifth to 15 September 2024) are quoted on the pages, but the calendar shows the ordinary dates.

The last useful day

The collection agency’s reading is applied to each due date: move to the next working day, add the five-day tolerance, move again if the fifth day is a holiday. Holidays are the national ones (1 and 6 January, Easter Monday, 25 April, 1 May, 2 June, 15 August, 1 November, 8, 25 and 26 December) plus Saturdays and Sundays. Checked examples: 31 July 2026 becomes 5 August 2026 as in the FAQs; 15 September 2024 becomes 23 September 2024; 30 November 2026 becomes 7 December 2026.

Estimating the amounts

The law requires equal instalments with 3% interest from 1 August 2026 (quinquies) or 1 April 2027 (local authorities) and 2% from 1 November 2023 (quater and readmission). For each period the calendar charges simple interest on the balance (annual rate times months elapsed over twelve) and finds the equal instalment that clears the debt; the last instalment absorbs rounding. The first quinquies and local instalments fall before interest starts. Example: €10,000 over 54 instalments gives €210.72 each, of which €48.14 is interest in the third, and €1,378.60 of interest overall. For the quater the first two instalments are 10% of the sum due and the other sixteen are equal: €522.27 on €10,000. A single readmission payment carries interest from 1 November 2023: €10,350.00 on €10,000. If an instalment falls below €100, the number of instalments is reduced until every one clears the threshold, as the FAQs say.

Lapsing

Quinquies and local authorities: you lapse by failing to pay, or underpaying, the single payment, two instalments whether consecutive or not, or the last one; lateness beyond five days counts only for the single and the last (paragraph 95 as amended). A payment covers the oldest open instalment (FAQ 12), so a skipped instalment never made up leaves the last one uncovered. Quater and readmission: a single instalment unpaid, short or over five days late is enough (paragraph 244). The check counts instalments already due at today’s date, by their last useful day.

Savings and instalment plans

The savings calculation does not estimate the items on the bill: it reads them from the document you enter. For taxes, contributions and local taxes you pay principal and costs and penalties, interest, late interest and the fee are written off; for fines the penalty stays and interest, surcharges and the fee are written off. The ordinary instalment plan uses an equal monthly instalment at 4.5% for tax debts and 4.65% for INPS debts, the instalment caps by year of request and the €120,000 threshold.

The tests

Calendars, last useful day, minimum instalment, quater and readmission plans, the FAQ lapse cases, savings and instalment-plan caps are automated tests (src/lib/engine/definizione.test.ts), rerun at every publication: a failing test blocks it.

What the site does not do

It does not read your bills or your plan: it works only on what you enter; the statement is binding.
It does not say whether a debt is time-barred or whether a bill is valid.
It does not anticipate a new rottamazione: as of 26 October 2026 no text has been published.
It sells no advice, paperwork service or loan and asks for no account, email or phone number.

Updates

Updates are manual, because the data only changes when a new text or a new version of the FAQs comes out: parameters are corrected, tests rerun and the site republished. Last reread: 26 October 2026. An error reported to contatti@ratecartelle.it is checked against the source, fixed and turned into a test. See the editorial policy.

All sources

Texts reread on 26 October 2026.

Method and sources