How the SIP calculator works
A SIP (systematic investment plan) is a way to invest a fixed amount in a mutual fund every month. Each instalment buys units at that day's price, so you buy more units when prices are low and fewer when they're high.
To project a SIP, the calculator assumes a steady yearly return and turns it into a monthly rate (the yearly rate ÷ 12). Each instalment is treated as invested at the start of the month and grows for every month left. Without a step-up this is the standard formula FV = P × ((1 + i)^n − 1) ÷ i × (1 + i), where P is the monthly amount, i the monthly rate and n the number of months.
For example, ₹10,000 a month for 10 years at an assumed 12% a year means ₹12 lakh invested and an estimated value of about ₹23.2 lakh. At an assumed 8%, the same SIP comes to about ₹18.4 lakh. That gap is why it's worth trying more than one return.