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Quarterly Income Tax Installment Calculator Sri Lanka

If you're self-employed: estimate your Q1–Q4 installments based on prior-year liability or current-year forecast.

Personal relief
Rs 1.8M
Slabs
6% → 36%
Interest AIT
10%
Return due
30 Nov 2026

Reflects Y/A 2025/2026Reviewed by TaxWiseLast updated 13 June 2026Source: Inland Revenue Act No. 24 of 2017, Inland Revenue Department

Calculator

Self-assessment installments

SET Q1–Q4 for Y/A 2025/2026. Each installment is one quarter of estimated annual tax.

Estimated annual tax payableRs 240,000

Use prior-year liability or current-year forecast.

Rs 0Rs 5,000,000
Result
Rs 60,000
Per quarter (equal split)
Q115 Aug 2025Rs. 60,000
Q215 Nov 2025Rs. 60,000
Q315 Feb 2026Rs. 60,000
Q415 May 2026Rs. 60,000

Deadlines: 15 Aug / 15 Nov / 15 Feb / 15 May for Y/A 2025/2026.

This is one piece of your return. See which schedules you file, which reliefs apply, and what the whole year comes to.

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SET installments tied to your live liability

As income changes through the year, TaxWise recalculates what each quarterly payment should be. You submit on the IRD e-Filing portal.

Start my returnReturn for Y/A 2025/2026 due 30 November 2026
In TaxWise
  • Forecast annual tax from actual income entered so far
  • SET Q1–Q4 deadlines from the active Y/A config
  • Record installments paid and balance due at filing
This calculator: Equal split of one annual figure. No mid-year revision or payment tracking.

Frequently asked questions

15 August, 15 November, 15 February and 15 May. A final balance payment is due 30 September after the year of assessment.

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Estimator disclaimerResults follow the Inland Revenue Act and the 2025 Amendment for Y/A 2025/2026 but are not tax advice. Rounding, missing inputs and simplified assumptions can change the final figure. Only a return you submit to the IRD counts.