Compound interest is the reason a deposit left alone for a decade grows faster than most people expect. In the first period you earn interest on the money you put in. In the second period you earn interest on the money you put in plus the interest you already earned. Repeat that enough times and the growth curve stops looking like a straight line and starts to bend upward.

The whole thing is captured by one formula, which is what the calculator above evaluates:

• A — the maturity amount, what you end up with.
• P — the principal, the lump sum you deposit at the start.
• r — the annual interest rate as a decimal, so 6.8% becomes 0.068.
• n — how many times a year interest is compounded (1 for annual, 4 for quarterly, 12 for monthly).
• t — the term in years.

The interest you actually earn is then just A − P. Everything else the calculator shows you — the year-by-year table, the total interest, the effect of dragging a slider — comes out of that single expression.

Suppose you deposit ₹1,00,000 for 10 years at 6.8% per year, compounded quarterly. Then P = 100000, r = 0.068, n = 4, and t = 10.

Almost doubling in ten years, and roughly ₹27,000 of that came from interest earning interest rather than from the original deposit. That gap is the entire argument for starting early and leaving money alone.

Two deposits can advertise the same rate and pay out different amounts, purely because one compounds more often. Here is the same ₹1,00,000 at 6.8% for 10 years under each frequency the calculator supports:

Monthly compounding beats annual by around ₹2,760 here — not life-changing, but free. The effect grows with both the rate and the term, which is why comparing the effective annual rate rather than the headline rate matters when you are choosing between products. At 6.8% nominal, quarterly compounding gives an effective rate of about 6.98%.

Simple versus compound

For comparison, the same ₹1,00,000 at 6.8% simple interest earns a flat ₹6,800 every year, reaching ₹1,68,000 after ten years. Compounding quarterly gets you to ₹1,95,352 over the same period. The difference of roughly ₹27,000 is entirely down to interest being reinvested rather than paid out.

The growth calculator answers one question well: if I put this amount away at this rate for this long, what do I end up with? That covers a lot of everyday planning.

• Comparing fixed deposit offers.Enter each bank’s rate, tenure, and compounding frequency and compare maturity values directly rather than trying to judge headline rates against each other.
• Working backwards from a goal. If you need a specific amount for a down payment, a wedding, or a car, adjust the principal and tenure sliders until the maturity value lands on your target.
• Modelling small-savings schemes. PPF, NSC, and similar lump-sum instruments follow the same compounding maths — set the rate and term to match the scheme.
• Understanding the cost of waiting. Run the same amount over 5, 10, and 15 years to see concretely what a few years of delay costs you.
• Everyday and technical maths. The scientific calculator handles expressions, trigonometry, logarithms, factorials, and constants, with a history you can reuse.

A maturity figure from any calculator is a clean number produced by a clean formula, and reality is messier. Before you rely on a result, be aware of what is deliberately left out:

• Tax. Interest income is generally taxable and may have tax deducted at source. The figures shown are gross, so your actual return will be lower.
• Fees and penalties. Breaking a deposit early usually means a reduced rate plus a penalty, which can wipe out much of the benefit of the longer term you were quoted for.
• Rate changes. The model assumes a fixed rate for the whole term. Floating-rate and renewable products do not work that way.
• Provider conventions. Day-count rules, rounding, and exactly when interest is credited vary between institutions and can shift the final figure slightly.
• Inflation. ₹1,95,352 in ten years will not buy what ₹1,95,352 buys today. For real purchasing power, subtract expected inflation from the rate before running the numbers.
• Recurring contributions. This is a lump-sum model. It does not handle recurring deposits or SIP-style monthly contributions.

Every figure you enter is processed locally in JavaScript on your own device. No amount, rate, tenure, or result is transmitted to a server, written to a log, or stored anywhere, so you can model real numbers rather than rounded stand-ins. Closing the tab discards everything. Details are in the privacy policy.