How we compare fixed-deposit rates

The two numbers we show

Hover any rate in the comparison table and you'll see two numbers per cell:

AER (the headline) — the effective annual rate of return, accounting for compounding. The number you should compare across banks.
coupon— the nominal annual rate the bank actually pays per period (when it differs from AER). The number you'll see on the bank's own rate sheet.

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.

Why they differ: it's the payout cadence

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.

The maths, per cadence

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.

Worked example: HNB 12-month FD, Monthly payout

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:

9.98% — the AER we computed for the Monthly cadence
coupon 9.55%— the bank's Monthly column verbatim

The 9.98% is derived from the bank's 9.55%:

AER = (1 + 0.0955 / 12)¹² − 1

= (1 + 0.00795833…)¹² − 1

= 1.09981 − 1

= 0.0998 = 9.98%

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.

Worked example: simple-interest at maturity, multi-year

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):

AER = (1 + 0.1125 × 2)^1/2 − 1

= (1.225)^0.5 − 1

= 1.1068 − 1

= 0.1068 = 10.68%

The bank's own column shows 10.70% — 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.

Why normalise to AER at all

Because every bank uses a different convention for its "headline":

Some lead with the Maturity rate (simple interest) — looks high but isn't annualised
Some lead with the Annually-paid rate — already annualised, no compounding
Some only publish per-cadence columns and let the user infer

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.

What the filter chips mean

Currency: LKR is the standard retail rate card. USD / GBP / EUR / AUD etc. are foreign-currency FDs (FCA), with their own per-bank rate cards — typically much lower than LKR (reflecting global yields, not local).
Payout: Cash-flow timing. At maturity locks all interest until term end. Monthly / Quarterly / Bi-annual / Annual pay periodically — useful if you need income but mathematically equivalent to Maturity if you reinvest.
Rate card: Standard = the public retail FD. Senior citizen = 60+ rate card (typically 25–50 bps premium). The eligibility & proof requirements come from each bank's terms.
Min deposit: Some banks reserve their top rates for larger deposits. Filtering by deposit size narrows the table to rate cards your balance qualifies for.

Special / promotional FDs

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.

Freshness & provenance

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.

Things we deliberately don't do

No paid placement. The same algorithm scores every bank; no bank pays for ordering.
No tax adjustment. WHT (withholding tax) and the SLDI (Sri Lanka Deposit Insurance) levy apply uniformly across banks. We quote the gross AER the bank publishes; your net depends on your tax band and is the same gap whichever bank you choose.
No projection.AER assumes you reinvest at the same yield — but FD rates change. We don't pretend to forecast where rates will move; the chart shows where they have moved.
No specialist instruments.CDs, treasury bills, and promotional Vishwa/Kalin-style premium products live outside the comparison surface. They're different instruments, not different rate cards.