How Is Recurring Deposit (RD) Interest Calculated?

A recurring deposit (RD) is one of the simplest ways to save: you commit to putting a fixed amount into the bank every month for a set period, and at the end you get back everything you paid in plus interest. It suits people who want the safety and guaranteed return of a fixed deposit but do not have a lump sum to lock away up front. The tricky part is the maths - because each monthly instalment is deposited at a different time, each one earns interest for a different length of time, and Indian banks compound that interest quarterly. This guide explains exactly how the maturity value is calculated so you can reproduce and check the figures in the RD Calculator.

The RD maturity formula

An RD is really a series of deposits, each compounding until the same maturity date. The first instalment earns interest for the full tenure, the second for one month less, and so on down to the final instalment, which earns interest for just one month. Rather than adding up every instalment separately, banks use a closed-form formula based on quarterly compounding:

• M = P × [ (1 + i)^n − 1 ] ÷ [ 1 − (1 + i)^(−1/3) ]
• where P is the monthly deposit, i is the quarterly interest rate (annual rate ÷ 400, as a decimal), and n is the number of quarters (tenure in months ÷ 3).

The (1 + i)^(−1/3) term in the denominator is what handles the monthly instalments inside each quarter - it spreads the quarterly compounding across the three months so that each deposit is credited interest fairly. This is why RD tenures are always entered in multiples of 3 months: the standard bank formula works in whole quarters. The total you actually pay in is simply P × months, and the interest earned is the maturity value minus that total.

Why quarterly compounding matters

Compounding frequency quietly changes your return. Indian banks credit and compound RD interest every quarter, so interest earned in one quarter starts earning its own interest in the next. If interest were compounded only once a year, your maturity value would be slightly lower for the same headline rate; compounded monthly, it would be slightly higher. Quarterly is the market standard, and it is what the RD Calculator assumes so its output matches the passbook figure your bank will show. The effect is small over a short tenure but grows with time - which is why a longer RD earns proportionally more interest than a short one at the same rate.

A worked example

Take the calculator's defaults: a 5,000 monthly deposit at 7.2% per annum for 24 months. First convert the inputs:

• Quarterly rate i = 7.2 ÷ 400 = 0.018.
• Number of quarters n = 24 ÷ 3 = 8.
• Total invested = 5,000 × 24 = 1,20,000.

Now plug into the formula. The numerator (1.018)^8 − 1 = 1.153406 − 1 = 0.153406. The denominator 1 − (1.018)^(−1/3) = 1 − 0.994071 = 0.005929. Dividing gives 0.153406 ÷ 0.005929 ≈ 25.874, and multiplying by the 5,000 monthly deposit:

• Maturity M = 5,000 × 25.874 ≈ 1,29,369.
• Interest earned = 1,29,369 − 1,20,000 = 9,369.

So two years of disciplined 5,000-a-month saving turns 1,20,000 of your own money into about 1,29,369 - roughly 9,369 of guaranteed interest. Stretch the same 3,000-a-month habit over five years at 6.7% and you deposit 1,80,000 and mature at about 2,14,097, earning 34,097 in interest. The longer horizon lets quarterly compounding do far more of the work. Try your own numbers in the RD Calculator to see how the tenure and rate move the result.

RD vs FD vs SIP

It is easy to confuse these three. A fixed deposit (FD) takes a single lump sum today and locks it for the whole term, so every rupee earns interest for the full period - an FD of the same total will always mature slightly higher than an RD, because the RD's money trickles in over time. An RD suits a monthly saving habit rather than a windfall. A systematic investment plan (SIP), by contrast, is not a deposit at all: it invests a fixed monthly amount into mutual funds, so the return is market-linked and not guaranteed. RD gives certainty and capital safety; SIP offers higher potential returns with real risk. If you are weighing the two, compare the guaranteed RD figure here against a market projection in the SIP Calculator, and use the FD Calculator for the lump-sum equivalent.

The tax rules on RD interest

RD interest is fully taxable. Unlike a PPF or the tax-free portion of some other schemes, the interest you earn on a recurring deposit is added to your income and taxed at your slab rate in the year it accrues. Banks also deduct TDS (tax deducted at source) at 10% if your total interest from RDs and FDs with that bank crosses the annual threshold in a financial year - you can submit Form 15G or 15H to avoid TDS if your total income is below the taxable limit. Note that TDS is not the final tax: if your slab rate is higher than 10% you owe the difference, and if it is lower you can claim a refund. Factor this in when comparing an RD's headline rate against tax-advantaged options like the PPF.

What the estimate assumes

The calculator gives the standard-formula maturity value, but a few real-world details can nudge it. It assumes every instalment is paid on time - a missed or late deposit reduces your interest and some banks levy a small penalty. It assumes the rate stays fixed for the whole tenure, which is how RDs work once opened, but the rate on offer changes between banks and over time, so shop around before you commit. Premature withdrawal usually attracts a penalty of around 0.5-1% on the applicable rate, so an RD is best treated as money you can leave untouched until maturity. Treat the output as an accurate estimate of the guaranteed maturity, and revisit the RD Calculator whenever your bank revises its rate.