Fixed Deposit Calculator
Compare simple and compound FD returns in LKR with maturity value, effective annual yield, post-tax outcome, and inflation-aware results.
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Inputs
Deposit setup
Start with the basic deposit details, then enable advanced mode for tax and inflation-aware analysis.
≈ 1 years
Advanced mode
Reveal tax, inflation, and real-return analysis without cluttering the core workflow.
Interest style
Maturity value
LKR 550,000.00
Interest earned
LKR 50,000.00
Effective annual yield
10.00%
Compounding-adjusted
Monthly equivalent interest
LKR 4,166.67
Growth
Deposit balance over time
The chart separates principal and accrued interest so you can see how compounding changes the outcome.
Comparison
How each compounding method changes the outcome
Use the same principal, rate, and term to compare simple and compound structures side by side.
| Method | Maturity | Interest | Effective yield |
|---|---|---|---|
| Simple | LKR 550,000.00 | LKR 50,000.00 | 10.00% |
| Monthly | LKR 552,356.53 | LKR 52,356.53 | 10.47% |
| Quarterly | LKR 551,906.45 | LKR 51,906.45 | 10.38% |
| Semi-Annual | LKR 551,250.00 | LKR 51,250.00 | 10.25% |
| Annual | LKR 550,000.00 | LKR 50,000.00 | 10.00% |
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Perspective
Why FD comparison is usually done badly
Most deposit ads emphasize the nominal annual rate, but what actually matters is the effective annual yield once compounding frequency is taken into account. Two deposits with the same headline rate can produce different maturity values.
Professionals also compare post-tax and inflation-adjusted outcomes. A deposit that looks attractive before tax may barely preserve purchasing power if inflation remains elevated.
This version lets casual users stay with the core inputs while advanced mode exposes the assumptions that matter when you are deciding between FDs, money-market funds, or Treasury instruments.
FAQ
Common questions
What formula is used for a fixed deposit maturity value?
Simple interest uses Principal x (1 + rate x time). Compound interest uses Principal x (1 + rate / n)^(n x time), where n is the number of compounding periods per year.
Why does compounding frequency matter?
More frequent compounding means interest is added back to the deposit sooner, which lets that interest begin earning additional interest. Monthly compounding therefore produces a higher effective annual yield than annual compounding at the same nominal rate.
Should I compare FD returns before or after tax?
For decision-making, compare after-tax results. Tax rules can change, but the investor only keeps the net interest after applicable withholding or other taxes.
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