Sri Lanka Savings Account Interest Calculator

Sri Lankan banks do not multiply your balance by the quoted rate once a year. They accrue interest on the daily closing balance and credit it monthly — the convention stated in the Central Bank of Sri Lanka's deposit-interest guidance and in every licensed bank's savings product terms. For a single day:

daily interest = balance × (annual rate ÷ 100) ÷ 365

For a month of N days at a steady balance B, that sums to B × (rate ÷ 100) × N ÷ 365. A 31-day month therefore earns more than a 28-day February at the same balance. But because the day counts across a non-leap year add up to exactly 365, a balance left untouched for a full year earns exactly B × rate gross — the day-count method only changes things month to month and when your balance moves. The calculator verifies its month-by-month loop against this closed form to the rupee.

The 10% AIT. On interest paid to resident depositors, the bank withholds Advance Income Tax before crediting it, raised to 10% with effect from 1 April 2025 (IRD Circular SEC/2025/E/03):

monthly AIT = monthly gross interest × 0.10
monthly net = monthly gross interest × 0.90

Reinvested vs paid out.Under “paid out” the net interest leaves the account each month, so the balance only grows by any top-up. Under “reinvested” the net interest is added to the balance, so next month accrues on a higher daily balance — interest earning interest. The effective net annual yield is derived from the actual growth, annualised: (final value ÷ principal contributed)^(12 ÷ months) − 1. With a monthly top-up this yield is a close approximation, since later contributions have had less time to earn.

If your annual assessable income does not exceed the Rs 1,800,000 personal relief, you may file a self-declaration so the bank stops withholding AIT (IRD Circular SEC/2025/E/02). The tool surfaces this as guidance and lets you model it by unticking the AIT option, but never assumes you qualify — by default it shows the deduction the bank actually makes.

• IRD Circular SEC/2025/E/03 — 10% Advance Income Tax on interest (from 1 April 2025)
• IRD — Circulars (incl. SEC/2025/E/02 self-declaration mechanism)
• Central Bank of Sri Lanka — deposit-interest / financial consumer guidance

The daily-balance method and the 10% AIT rate on this page were last cross-checked against the IRD and CBSL sources on 2026-07-11. The page is reviewed after any change to the AIT rate or the personal relief threshold. Quoted bank rates are user-entered and not verified by this tool.