How a SIP calculator works, with the formula Indian sites actually use

The number everyone is trying to match

A systematic investment plan adds money on a date every month. If the return is steady, the maturity has a closed form. For a payment at the start of each month it is P × (((1 + r)^n − 1) / r) × (1 + r). Here r is the annual return divided by 12, and n is the number of months.

₹5,000 a month at 12% for 10 years is 120 payments of ₹5,000, so you invest ₹6,00,000. The formula produces about ₹11.62 lakh. Wealth gained is about ₹5.62 lakh. ClickZM's SIP calculator uses that same beginning-of-month convention, which is what most Indian fund calculators show.

Step-up and inflation are separate questions

A step-up SIP raises the instalment once a year. There is no single tidy formula, so the calculator compounds each instalment for the months left after it is paid. A 10% step-up on a ₹10,000 SIP makes the second year ₹11,000 a month.

Inflation does not change the rupee maturity. It divides that maturity by (1 + inflation)^years so you can see today's purchasing power. A large future number can still be a modest lifestyle if prices have moved.

What the calculator leaves out

It does not subtract tax, exit load or a missed instalment. Equity fund gains have their own rate after the annual exemption. The return you type is an assumption, not a scheme document. Use the result to set a monthly amount, then compare the same amount in the FD and RD calculators if you want a fixed rate next to it.