An FD interest calculation needs more than an annual percentage. The amount deposited, start date, maturity date, compounding rule and payment schedule determine what the arithmetic represents. A bank's deposit confirmation supplies those terms for a particular deposit.
The figures below are fictional and use an assumed 6% annual rate. They are not current offers, expected returns from another investment or a comparison of banks.
A simple one-year example
Suppose ₹1,00,000 earns simple interest at 6% for exactly one year. Interest is principal multiplied by annual rate multiplied by time in years. The calculation is ₹1,00,000 × 0.06 × 1, producing ₹6,000.
If all that interest is paid at maturity, total cash received is ₹1,06,000 before any deductions. If interest is paid out during the year, the maturity credit can contain only the returned principal. The total receipts over the term still need to include the earlier interest payments.
A six-month illustration using a time fraction of one half produces ₹3,000. That is a simplified year-fraction example. Actual bank calculations can use completed months, actual days or separate treatment for a remaining partial period.
Quarterly compounding changes the result
Now assume the same fictional ₹1,00,000 stays invested for four complete quarters and interest compounds quarterly. Divide 6% by four to obtain 1.5% per quarter. Each quarter's interest stays in the deposit and earns interest during later quarters.
The one-year amount is ₹1,00,000 × (1 + 0.06 ÷ 4) raised to the power of four. Rounded to paise, the result is ₹1,06,136.36 before deductions. The interest is ₹6,136.36.
The extra ₹136.36 comes from interest earned on earlier interest. It does not come from changing the assumed annual rate. Annual compounding at 6% over a single year produces ₹1,06,000 because there is no earlier within-year addition to compound.
A real deposit has date conventions
SBI's published deposit terms describe quarterly compounding for certain reinvestment deposits and a separate daily calculation for a remaining broken period. Axis Bank also publishes a calculation methodology. These are examples of institution-specific terms, not a universal formula for every Indian FD.
An FD running from one date to another can contain complete quarters plus extra days. Substituting a rounded tenure of 1.5 years for the bank's actual schedule can produce a different answer. Leap years, rounding and the precise interest payment dates can create further differences.
The booked rate also needs to remain attached to the original deposit. A current rate displayed on a website describes an offer at that time. Replacing a historical deposit's rate with it rewrites the contract in the tracker.
Gross interest and bank credits are different records
A maturity estimate usually describes an amount under stated assumptions before tax effects, unless it explicitly says otherwise. A bank credit can reflect deductions or earlier payouts. The difference requires the deposit advice and interest statement rather than an assumption that the formula failed.
Recording gross interest, deductions and net receipts separately preserves what each amount means. This article does not determine the tax treatment or deductions that apply to a reader's deposit.
FinTarget's Fixed Deposits guide covers principal, dates, rate and a maturity amount override. Its default estimate uses annual compounding. It does not automatically reproduce quarterly schedules, every bank's day-count method or premature closure terms. An amount taken from the bank's own confirmation can be entered as the override while the supporting document retains the calculation details.