How a SIP grows
Each month the calculator adds your instalment at the start of the month. It then adds one month of growth. It repeats that for every month you stay in.
AMFI describes a SIP as a fixed amount paid into a mutual fund at a set interval, often once a month. The fund buys units at that day’s price. This calculator does not use a changing price. It uses the single return you type.
The formula in plain words
For a flat SIP, maturity equals the monthly amount, times (((1 + monthly rate) to the power of the months, minus 1) divided by the monthly rate), times (1 + monthly rate). The monthly rate is the yearly return divided by 12. The last part is there because the money goes in at the start of the month.
A step-up has no short formula. The monthly amount rises once a year, and each new amount follows the same month-by-month rule. Today’s rupees are the maturity divided by (1 + inflation) to the power of the years. The SIP itself does not rise with inflation unless you set a step-up.
A worked example
₹10,000 a month, 12% a year, 10 years, no step-up. You put in ₹12,00,000. The maturity is ₹23,23,391. The estimated return is ₹11,23,391. At 6% inflation, that maturity is about ₹12,97,369 in today’s rupees.
AMFI’s investor booklet uses ₹1,000 a month at 10% for 25 years and shows about ₹13.38 lakh, from ₹3 lakh put in. This calculator gets ₹13,37,890. AMFI marks that figure as an illustration, not a promise.
Tax, on a simpler case: a long-term gain of ₹2.25 lakh. Section 198 of the Income-tax Act, 2025 taxes equity-fund gains above ₹1.25 lakh at 12.5%. The tax is ₹12,500. Cess at 4% is ₹500. The total is ₹13,000. Units held for 12 months or less are short-term under section 2(101), and Section 196 taxes them at 20%.
The return you type here is a compound rate. The CAGR calculator finds that rate from a start value and an end value.
If the SIP is meant to cover your spending one day, the FIRE calculator turns expenses into a corpus and the monthly SIP that gets you there.