Sri Lanka Tax Penalty & Interest Calculator

The estimator applies three independent statutory rules and sums the results. Each rule is implemented exactly as worded in the Inland Revenue Act No. 24 of 2017 (consolidated) and the VAT Act No. 14 of 2002, with citations exposed on every output line so you can audit the working against the source.

Step 1 — Days and months overdue

Both rules count time in months, with any part of a month treated as a full month — this is the explicit wording of section 159 and is the convention IRD uses in its own worked illustrations. The calculator converts elapsed days to months using the average Gregorian month of 30.4375 days and rounds up: monthsOverdue = ceil(daysLate ÷ 30.4375). The late-filing per-month addon under section 178 uses complete elapsed months instead (floor of the same ratio), which matches the IRD example showing that a 30-day-late return attracts only the flat Rs 50,000 base, not the Rs 10,000 per-month addon.

Step 2 — Interest on default (IRA s.159 / VAT s.26)

Section 159 of the Inland Revenue Act states that interest is payable on any unpaid tax at the rate prescribed for each period; the IRD's current penalty schedule pins this at 1.5% per month or part of a month, applied to the original outstanding amount. Interest is simple, not compounding — the section is worded as a rate-per-month charge, not as an accruing balance, and the IRD's public illustrations apply the rate to the original principal each month. The same 1.5% per-month rate applies to VAT under section 26 of the VAT Act, to withholding tax shortfalls, to APIT remittances missed by employers, and to SSCL under the equivalent administrative framework.

Step 3 — Late-payment penalty (IRA s.179 / VAT s.26)

Section 179 imposes a flat 10% of the unpaid tax when payment is more than 14 days late, plus a further 2% for every additional month or part of a month. The 14-day grace window applies only to the percentage penalty — interest still accrues for any delay. The formula implemented is penalty = principal × 10% + principal × 2% × max(0, months − 1), gated on daysLate > 14. For VAT the corresponding mechanic lives in section 26 of the VAT Act with identical 10% + 2% rates.

Step 4 — Late-filing penalty (IRA s.178 / VAT s.27)

Section 178 charges Rs 50,000 as a flat base when a return is not filed by the due date, plus Rs 10,000 for each complete month the return remains outstanding. When the cap toggle is on, the total is capped at the lower of the assessed tax or Rs 400,000 — this matches IRD's discretionary practice for first-time defaulters. Section 27 of the VAT Act applies the same Rs 50,000 + Rs 10,000 per-month formula to late VAT returns. The late-filing penalty is independent of the late-payment penalty: filing on time but paying late attracts only s.179, while filing late but paying on time attracts only s.178. Defaulting on both stacks the two.

Cross-check and edge cases

The total is computed twice using independent code paths — once as a direct formula and once by summing the month-by-month accrual table — and the result panel shows "Cross-checked · 2 methods" when the two agree to within one rupee. Three edge cases are handled deliberately: (1) payment exactly on the 14th day attracts interest but zero s.179 penalty; (2) a principal of zero or negative input is rejected with an actionable error rather than silently calculating; and (3) due dates before 1 April 2017 are refused because they fall under the older Inland Revenue Act No. 10 of 2006 with different rates. For amounts above Rs 1,000,000,000 the calculator stops and recommends contacting IRD directly — the formula is linear and would still produce a number, but practitioner sense-checking is more useful than another spreadsheet output at that scale.

Three end-to-end scenarios mapped to common Sri Lankan defaults. Punch each into the calculator above — the totals match to the rupee.

• Inland Revenue Act No. 24 of 2017 (consolidated) — IRD
• IRD — Penalties & interest schedule with worked illustrations
• Value Added Tax Act No. 14 of 2002 (consolidated) — IRD
• Inland Revenue Department of Sri Lanka — official site

The rate schedule on this page was last cross-checked against the consolidated IRA and the IRD penalty publication on 2026-05-16. The page is reviewed after every Finance Act and every Inland Revenue (Amendment) Act.