An FD interest calculator estimates the amount payable on a fixed deposit from four inputs: the deposit, annual interest rate, tenure and interest treatment. For a cumulative deposit, interest added to the balance earns further interest. For a payout deposit, interest is paid out during the term, so the amount returned at maturity can be just the original deposit.
The distinction matters when two calculation screens show different maturity amounts for the same deposit. One may include accumulated interest while the other assumes that interest has already been paid to the depositor. The example below isolates the arithmetic, using an assumed rate rather than a current bank offer.
| Input | Assumption |
|---|---|
| Deposit | Rs 1,00,000 |
| Annual rate | 7%, assumed throughout |
| Tenure | 3 complete years |
| Compounding | Quarterly, with all interest reinvested |
| Calculated maturity amount | Rs 1,23,143.93 |
| Calculated interest | Rs 23,143.93 |
How is FD interest calculated?
The HDFC Bank FD calculator gives the compound-interest formula as A = P × (1 + r/n)^(n × t). Here A is the maturity amount, P is the deposit, r is the annual rate expressed as a decimal, n is the number of compounding periods each year and t is the term in years. Thus 7% must be entered as 0.07 in this formula, not as 7.
For this illustration, the calculation is 1,00,000 × (1 + 0.07/4)^12 = Rs 1,23,143.93, rounded to two decimal places. Subtracting the original Rs 1,00,000 leaves Rs 23,143.93 of interest. The exponent is 12 because three years contain 12 quarters.
The first quarter makes the process easier to see. Interest is Rs 1,750, taking the balance to Rs 1,01,750. The second quarter earns Rs 1,780.625 on that larger balance. Before rounding, the balance becomes Rs 1,03,530.625. The extra interest comes from including the previous quarter's interest in the next calculation.
Simple interest versus quarterly compounding
ICICI Bank's interest explainer distinguishes simple interest from compound interest. With the annual rate written as a decimal, simple interest is P × r × t. On the same assumed Rs 1,00,000 at 7% for three years, that is Rs 21,000. Principal plus interest would therefore total Rs 1,21,000.
Quarterly compounding adds Rs 2,143.93 to that illustrative total. Annual compounding under the same assumptions would produce Rs 1,22,504.30, while monthly compounding would produce Rs 1,23,292.56. These are mathematical comparisons, not descriptions of three products available from a bank.
The quoted annual rate and the effective annual yield also differ. At 7% compounded quarterly, the one-year multiplier is (1 + 0.07/4)^4. Subtracting one and multiplying by 100 gives approximately 7.1859%. That calculation assumes every interest credit stays in the deposit.
Why does an FD calculator show only the principal at maturity?
HDFC Bank explains that with its monthly or quarterly payout option, interest goes to the linked account during the deposit period. The maturity amount then equals the principal. To understand the total cash received, add the separate interest payments to the final principal repayment. Do not compare that final payment alone with the maturity value of a cumulative deposit.
A reproducible calculation needs the same payout setting, deposit dates and tenure as the actual FD. HDFC labels its calculator result approximate, excludes TDS from the estimate and directs customers to the FD advice for the exact maturity amount. This article's numbers likewise exclude deductions and assume no early closure.
For related financial context, see our guides to repo-rate changes and deposits, education-loan eligibility and SEBI's mutual-fund portfolio framework.
