Sri Lanka Quarterly Income Tax Installment Calculator — Y/A 2025/26

Sri Lanka's Inland Revenue Act No. 24 of 2017 (Section 90) requires anyone whose income is not fully covered by employer-withheld APIT to pay their income tax in four equal installments during the year of assessment. If all your income is salary and your employer already deducts the full liability through the monthly APIT tax calculator, you have nothing to file here. Self-assessment installments exist for the income the payroll never sees — freelance fees, professional practice, business profit, rent, and foreign remittances. The framework has five moving parts; the calculator above handles all of them so you can plan cashflow rather than do arithmetic.

1. Estimate annual tax. Apply the IRD's Y/A 2025/26 progressive brackets to your projected annual taxable income (gross income minus the Rs 1,800,000 personal relief): 6% on the first Rs 1,000,000, 18% on the next Rs 500,000, 24% on the next Rs 500,000, 30% on the next Rs 500,000, and 36% on the balance.
2. Choose your estimation basis (Section 90(2)).Either (a) a reasonable estimate of the current year's tax (Step 1 above), or (b) 90% of the prior year's actual tax paid. The 90% method is useful if this year's income is hard to project but you have a stable history. If your income is mostly freelance fees, the freelancer tax calculator is a quick way to build the current-year estimate that feeds Step 1.
3. Divide by four.Each installment is one-quarter of the estimated annual liability, rounded to the nearest rupee. The IRD's paying-in slip won't accept fractional cents.
4. Apply the statutory due dates.Quarters fall on 15 August, 15 November, 15 February, and 15 May. If a date is a weekend or gazetted public holiday, the next working day applies (Interpretation Ordinance, Section 7). Pay through any BoC, People's Bank, HNB, Sampath, or NSB counter or via the IRD e-Services portal using payment code 02 (Self-Assessment).
5. File the Section 93 return and settle the balance. By 30 September following year-end, file your final return; the balance (actual annual tax minus the four installments paid) is due the same day. Over-payment credits forward; under-payment beyond the 90% safe harbour can attract interest under Section 178(2).

Section 178 interest on late payment is computed daily as principal × rate × (days / 365), where the rate is set by the Commissioner-General — currently CBSL Standing Lending Facility Rate + 2 percentage points (around 15.5%p.a. as of mid-2026). The calculator's late-payment toggle uses this rate as an illustrative figure; the official slip should be confirmed against the IRD's current rate notice. If you have already missed a date and want a standalone estimate, the tax penalty calculator walks the interest and additional-penalty rules in more detail.

Which method should you pick?

The two Section 90(2) bases exist for different situations, and picking the right one is the single biggest lever on your quarterly cashflow. The current-year estimate ties each installment to what you actually expect to earn this year — it is the honest choice when income is growing, because it keeps your final Section 93 balance close to zero and avoids a large September top-up. The 90%-of-prior-year basis, by contrast, is a legal safe harbour: pay four installments of one-quarter of 90% of last year's actual tax and you are treated as having made a proper estimate even if this year turns out higher. That protects you from Section 178(2) interest on the shortfall. The trade-off is that if your income has fallen, the prior-year basis over-pays and ties up cash until you reclaim it — so a shrinking practice usually prefers the current-year estimate, while a rising one often prefers the 90% safe harbour. The calculator runs both side by side so you can compare the quarterly figure before you commit.

Edge cases the calculator handles

Three boundary conditions trip people up. First, income below relief: if projected income is at or under the Rs 1,800,000 personal relief, taxable income is zero, annual tax is zero, and no installment is due — you still file a NIL return at year-end. Second, the bracket boundary: because Section 90 mandates one-quarter of the annual liability (not tax on one-quarter of income), a taxpayer whose taxable income lands exactly on a slab edge — say Rs 1,000,000, the top of the 6% band — pays a clean quarter of the whole-year figure, with no partial higher-rate slice. Third, shared relief: if you draw both a salary and freelance income, your PAYE employer may already apply part of the statutory relief. Enter only the unused slice in the relief field so the same Rs 1,800,000 is not deducted twice. Rental landlords should note that net rent after the 25% notional repair allowance is added to this projected income — the rental income tax calculator produces that net figure for you.

Before your first installment is due you need a Taxpayer Identification Number (TIN). If you have never registered, apply through the IRD e-Services portal at eservices.ird.gov.lk or at any IRD regional office; a National Identity Card and proof of income source are enough for an individual. Once you hold a TIN, the four installments are paid on the Self-Assessment Paying-In Slip under payment code 02. You can pay over the counter at Bank of Ceylon, People's Bank, HNB, Sampath, or NSB, or through the online-banking apps of the banks that support Self-Assessment payments. Keep every slip: the IRD reconciles what you paid quarter by quarter against the final return, and a missing slip is the most common cause of a disputed balance.

Four habits keep you out of trouble. First, revise mid-year if your income runs ahead of the estimate — raising an installment is free, and it shrinks the September balance and any interest on it. Second, diarise the dates: 15 August, 15 November, 15 February, and 15 May, with the final Section 93 return on 30 September. Third, net down rent and business income correctly before you project, because installments are sized on taxable — not gross — income. Fourth, file even a NIL return: if your income falls below the relief and no installment is due, the year-end return still has to be lodged. Treat the figures on this page as planning estimates and confirm the current rate notice and any amendment before you settle with the IRD.

• IRD — Self-Assessment Payment Notice (quarterly due dates)
• Inland Revenue Act No. 24 of 2017 (consolidated — Sections 90, 93, 178)
• IRD — Tax Chart for Y/A 2025/26
• Inland Revenue Department of Sri Lanka — official site

Calculation methodology and statutory dates on this page were last cross-checked against the IRD's self-assessment notice on 2026-05-16. The page is reviewed every April and after any Inland Revenue Amendment Act.