Sri Lanka · Methodology
Banks publish FD rates in different shapes. Some lead with a single headline number, others publish a column per payout cadence. To compare apples-to-apples, we normalise every bank to the same metric: Annual Effective Rate (AER). This page explains the maths, with worked sums against HNB's actual published table.
Open any rate in the comparison table (hover on desktop, tap on mobile) and you'll see two numbers per cell:
When AER and coupon are the same (≤ 5 bps apart), we hide the coupon line. When they differ, both are shown so you can verify our number against the bank's.
An FD pays interest either at maturity (lump sum at the end) or periodically (monthly, quarterly, semi-annually, annually). The payout cadence changes the effective return because periodic payouts can be reinvested. Banks publish a separate nominal rate per cadence to reflect this, but only one (or none) of those rates is the AER directly.
With nominal annual rate r (as a decimal) and n payouts per year:
| Payout | n | AER formula |
|---|---|---|
| Monthly | 12 | (1 + r/12)¹² − 1 |
| Quarterly | 4 | (1 + r/4)⁴ − 1 |
| Semi/bi-annual | 2 | (1 + r/2)² − 1 |
| Annual | 1 | r |
| At maturity (simple interest) | — | (1 + r · T)1/T − 1, where T = tenor in years |
All formulas assume periodic payouts are reinvested at the same yield, the conventional benchmark used across the industry to compare rates fairly.
HNB's published table for a 12-month LKR fixed deposit on 2026-06-10:
| Column | Value | Meaning |
|---|---|---|
| Monthly | 9.55% | Nominal annual rate, paid in 12 monthly installments of 0.7958% each. |
| Maturity | 10.00% | Simple-interest annual rate, full amount paid at end of term. |
| Annual Effective Rate (HNB's column) | 10.00% | HNB's headline AER, equivalent to Maturity for this row. |
Our display for the same row, with Monthly payout selected:
The 9.98% is derived from the bank's 9.55%:
Note: 9.98% is what you earn if you reinvest each monthly payout at the same rate. If you spend the payouts instead, you earn the nominal 9.55%. The bank's own "Annual Effective Rate" column shows 10.00%, but that's their AER for the Maturity option, not the Monthly option. They publish only one headline AER and don't break it down per cadence; we do.
HNB's 24-month FD pays 11.25% as a Maturity rate. That is simple interest: you deposit Rs 100,000, earn 11.25% × 2 = 22.5% over the 2 years, and walk out with Rs 122,500. To express this as a comparable annual rate (so you can stack it next to a 1-year FD):
The bank's own column shows 10.70%, the same number rounded differently. Our At-maturity AER for 24-months matches the bank's headline within ~2 bps in both directions across the corpus.
Because every bank uses a different convention for its "headline":
If we displayed each bank's "headline" verbatim, you'd compare 11.25% (Maturity) vs 10.55% (Annually) vs 9.55% (Monthly), none of which represent the same thing. By computing AER per payout cadence, every cell is the "effective annual return for this option," comparable across banks and tenors.
Some banks publish off-cycle "Special" FD products with tenors that don't fit the standard 1m / 3m / 6m / 12m / 2y ladder (4-month, 9-month, 15-month, etc.). These usually come with constraints (non-renewable, may require a fresh deposit each time). We surface them under the same currency-tenor key shape so they appear inline in the comparison; the bank's terms still apply.
Every rate carries a last observedtimestamp on the bank row. Banks revise FD rates roughly weekly when they revise at all; anything more than 7 days old is tagged amber, more than 14 days red. The number we store is what the bank's own rate page published on the observed date. Re-extraction happens daily, but re-stamping only occurs when the bank's published date moves forward.
Tap any bank to see its full term structure, the bank's stated terms (early withdrawal, auto-renewal, senior bonus details), and a direct link to the bank's own page.