Overview
A fixed deposit's maturity amount isn't just principal plus a flat percentage. It's compound interest, and how often that interest gets folded back into your principal changes the final number more than most depositors realize. Two FDs quoting the same "7% per annum" can mature to different amounts depending on whether the bank compounds quarterly, monthly, or annually.
This walkthrough covers the exact formula banks use, why compounding frequency matters, and how payout FDs (which pay interest out regularly instead of reinvesting it) calculate differently from the standard cumulative FD. Use the Fixed Deposit Calculator alongside this to check your own numbers instantly.
What You Need
- Principal amount, the lump sum you're depositing
- Interest rate, the annual rate quoted by your bank (check whether it's the same for your tenure and deposit amount, since rates vary by slab)
- Tenure, how long the FD runs, in months or years
- Compounding frequency, quarterly is the default at most Indian banks, though some offer monthly or annual
- Payout mode, cumulative (interest reinvested, paid at maturity) or payout (interest paid out monthly/quarterly, principal returned at maturity)
Steps
Step 1: Confirm which type of FD you have
The calculation splits into two completely different paths depending on payout mode. A cumulative FD reinvests every interest calculation back into the principal, so your money compounds for the full tenure. A payout FD pays interest out on a fixed schedule instead, which means it never compounds. You get simple interest each period, and your principal comes back untouched at maturity. Check your FD's terms before proceeding, since using the wrong formula gives you a meaningfully wrong number.
Step 2: Apply the compound interest formula (cumulative FDs)
For a cumulative FD, the maturity formula is:
A = P × (1 + r/n)^(n×t)
Where:
- A = maturity amount
- P = principal deposited
- r = annual interest rate (as a decimal)
- n = compounding frequency per year (4 = quarterly, 12 = monthly, 1 = annually)
- t = tenure in years
Worked example: ₹1,00,000 deposited at 7% per annum for 5 years, compounded quarterly (n = 4):
r/n = 0.07 / 4 = 0.0175 per quarter
n×t = 4 × 5 = 20 quarters
A = 1,00,000 × (1.0175)^20 = ₹1,41,478
Total interest earned: ₹1,41,478 − ₹1,00,000 = ₹41,478. Effective annual yield: (1,41,478 ÷ 1,00,000)^(1/5) − 1 = 7.19%, slightly above the nominal 7% rate, purely from the effect of quarterly compounding.
Step 3: Calculate simple interest for payout FDs
If your FD pays interest out monthly or quarterly instead of reinvesting it, the calculation is much simpler, since there's no compounding at all:
Total Interest = P × r × t
On the same ₹1,00,000 principal at 7% for 5 years with monthly payouts: Total Interest = 1,00,000 × 0.07 × 5 = ₹35,000 over the full tenure, or roughly ₹583 paid out each month. That's meaningfully less than the ₹41,478 a cumulative FD earns over the same period. Payout FDs trade a lower total return for regular cash flow.
Step 4: Account for compounding frequency differences
The same nominal rate produces different maturity amounts depending on how often interest compounds. For ₹1,00,000 at 7% over 5 years:
| Compounding | Maturity Amount | Effective Yield |
|---|---|---|
| Annually (n=1) | ₹1,40,255 | 7.00% |
| Quarterly (n=4) | ₹1,41,478 | 7.19% |
| Monthly (n=12) | ₹1,41,763 | 7.23% |
The jump from annual to quarterly compounding adds over ₹1,200 to the same deposit; the further jump to monthly adds much less. Each step up in frequency captures a shrinking additional benefit, which is why quarterly compounding, the default at most Indian banks, already gets you most of the way there.
Step 5: Check the effective yield, not just the quoted rate
Banks quote the nominal annual rate on their FD products, but the number that actually matters for comparing FDs across banks is the effective yield:
Effective Yield = (Maturity Amount ÷ Principal)^(1/t) − 1
Two FDs advertising "7%" can carry different effective yields if one compounds quarterly and the other monthly. Ask for the compounding frequency before comparing quoted rates across banks. The headline rate alone doesn't tell the full story.
Common Mistakes to Avoid
Assuming all FDs compound the same way. Compounding frequency varies by bank and product. Don't assume quarterly just because it's common; check your specific FD's terms.
Confusing quoted rate with effective yield. The rate on your FD receipt is nominal. Your actual annualized return is always slightly higher for cumulative FDs, and that gap widens with more frequent compounding.
Applying the compound formula to a payout FD. Payout FDs use simple interest per period since the interest gets withdrawn, not reinvested. Using the compound formula here overstates the maturity amount, since a payout FD's principal never actually grows.
Ignoring TDS on the way to your final number. This formula gives you the pre-tax maturity amount. FD interest is fully taxable at your slab rate, and banks deduct TDS once your interest income crosses ₹40,000 a year with that bank (₹50,000 for senior citizens). Plan for that separately.
Forgetting that early withdrawal breaks the calculation. This formula assumes the FD runs its full contracted tenure. Breaking it early triggers a recalculated, usually lower, rate plus a penalty, producing a maturity amount below what this formula projects.
Formula & Methodology
Cumulative FD (compound interest):
A = P × (1 + r/n)^(n×t)
Total Interest = A − P
Payout FD (simple interest per period):
Total Interest = P × r × t
Periodic Payout = (P × r) / (number of payouts per year)
Effective annualized yield:
Effective Yield = (A ÷ P)^(1/t) − 1
For a full breakdown of the variables and a step-by-step derivation, see the FD Maturity Formula page. If you're weighing a lump sum FD against a monthly recurring deposit for the same savings goal, How to Calculate RD Maturity Amount walks through the equivalent calculation for RDs, and FD vs RD: Which Is Better for Short-Term Savings? compares the two directly.