How to calculate SIP returns with an example

In this guide

This guide explains the three inputs a SIP calculation needs, the formula, a complete worked example, how the CalPaisa SIP Calculator performs the same calculation, and the mistakes that make SIP estimates misleading.

• The three inputs: monthly investment, period, expected return
• The three outputs: invested amount, maturity value, estimated gains
• The formula and a worked example
• Assumptions and common mistakes

The three inputs

Every SIP estimate starts from the same three numbers. Changing any one of them changes the result, so it helps to understand what each represents.

• Monthly investment (P): the fixed amount you invest each month.
• Investment period: how many years you will keep investing; multiplied by 12 it gives n, the number of instalments.
• Expected annual return: an assumed average yearly growth rate. Divided by 12 and by 100 it gives i, the monthly rate.

The three outputs

A SIP calculation produces three figures. The total amount invested is simply P × n — the money that leaves your account. The estimated maturity value (M) is what those instalments could grow to at the assumed rate. The estimated gain is M minus the total invested.

Only the first of these is certain. The maturity value and gain both depend on the assumed rate, and market-linked returns will not follow a fixed rate in practice.

The SIP formula

The standard SIP future value formula assumes each instalment is invested at the start of the month: M = P × [((1 + i)ⁿ − 1) ÷ i] × (1 + i).

The bracketed part adds up the growth of every instalment, each compounding for a different number of months. The final × (1 + i) reflects that each instalment is invested at the start of its month, so it earns one extra month of growth.

Worked example: ₹10,000 a month for 10 years

Take a monthly investment of ₹10,000 for 10 years at a hypothetical assumed return of 12% a year.

Step 1 — monthly rate: i = 12 ÷ 12 ÷ 100 = 0.01. Step 2 — number of instalments: n = 10 × 12 = 120. Step 3 — growth factor: (1.01)¹²⁰ ≈ 3.3004. Step 4 — apply the formula: M = 10,000 × [(3.3004 − 1) ÷ 0.01] × 1.01 ≈ ₹23,23,391.

Step 5 — total invested: ₹10,000 × 120 = ₹12,00,000. Step 6 — estimated gain: ₹23,23,391 − ₹12,00,000 = ₹11,23,391.

How the CalPaisa SIP Calculator performs the calculation

The SIP Calculator applies exactly this formula: it converts your annual rate to a monthly rate (annual ÷ 12), treats every instalment as invested at the start of the month, and compounds monthly. It shows total invested, estimated returns and maturity value, plus a year-by-year breakdown so you can see the balance build.

It does not deduct expense ratio, exit load or tax, and it does not adjust for inflation. Those are left out so the core growth is easy to see, but they all reduce what you actually keep.

Going further

If you plan to raise your instalment each year, the Step-Up SIP Calculator applies a yearly increase on top of the same maths. To compare with a one-time investment growing at a fixed rate, use the Compound Interest Calculator. And to turn a fund's actual start and end values into an annual growth rate, the CAGR Calculator is the right tool — a SIP's real return is usually measured as XIRR, because each instalment is invested on a different date.

Common mistakes when calculating SIP returns

These errors make SIP estimates look better or worse than they really are.

• Using the annual rate directly instead of the monthly rate in the formula.
• Confusing the estimated gain with the maturity value.
• Treating the assumed rate as a promised return.
• Ignoring costs, tax and inflation when comparing with a goal.
• Using CAGR to judge a SIP's actual performance instead of XIRR.

Conclusion

Calculating SIP returns comes down to a monthly rate, the number of instalments and one formula. Run the estimate at a few different rates rather than one optimistic figure, and read the result as a range of possibilities, not a guarantee.