FD Formula

Finance Formula • Published on July 30, 2026 • Last updated July 30, 2026

Mathematical Equation

$$A = P \times \left(1 + \frac{r}{n}\right)^{nt}$$

Variable Definitions

A

Final maturity amount (principal + interest)

P

Principal deposit amount invested

r

Annual nominal interest rate (as a decimal)

n

Compounding frequency per year (standard bank FDs compound quarterly, so n = 4)

t

Deposit tenure in years

Detailed Explanation

In-Depth Guide

Key Concept

A Fixed Deposit (FD) is a secure investment offered by banks and financial institutions where you deposit a lump sum for a fixed tenure at a guaranteed interest rate.

FDs usually calculate compound interest on a quarterly basis.

It offers steady, predictable growth on capital.

How to Calculate: Step-by-Step

1. Identify the principal deposit ($P$). 2. Identify the bank's annual interest rate ($R$) and convert to decimal ($r = R / 100$). 3. Identify the compounding frequency ($n = 4$ for quarterly, which is standard). 4. Identify the tenure in years ($t$). 5. Calculate the maturity amount ($A$) using the formula: $A = P \times (1 + r/n)^{n \times t}$. 6. Subtract the principal ($P$) from ($A$) to find the total interest earned.

Worked Calculation Example

You invest $20,000 in a fixed deposit for 3 years at an annual interest rate of 7%, compounded quarterly: - Principal ($P$) = $20,000 - Annual nominal rate ($r$) = 7% = 0.07 - Compounding frequency ($n$) = 4 (quarterly compounding) - Tenure ($t$) = 3 years - Calculate using the formula: $$A = 20,000 \times \left(1 + \frac{0.07}{4}\right)^{4 \times 3} = 20,000 \times (1.0175)^{12}$$ $$(1.0175)^{12} \approx 1.2314$$ $$A \approx 20,000 \times 1.2314 = \$24,628.78$$ - Total Interest Earned = $24,628.78 - $20,000 = $4,628.78

Common Use Cases

  • Calculating low-risk bank deposit maturity values
  • Comparing different bank interest rates and tenures
  • Retirement asset planning using steady-yielding vehicles

Frequently Asked Questions

Yes, premature withdrawals are usually allowed, but banks apply a penalty (typically 0.5% to 1%) reducing the effective interest rate earned.

Yes, the interest income is fully taxable under "Income from Other Sources" based on the investor's tax slab. Tax Deducted at Source (TDS) is deducted if interest exceeds specified thresholds.

FD Laddering is a strategy where you split your total investment corpus into multiple FDs with different maturity periods (e.g., 1-year, 2-year, 3-year). As each FD matures, you reinvest it, ensuring liquidity and optimizing interest rate cycles.

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