The SIP formula
The standard SIP future-value formula (annuity-due):
FV = M · [((1+i)^n − 1) / i] · (1+i)
- M — monthly investment
- i — monthly rate (annual ÷ 12 ÷ 100). A 12% annual return gives i = 0.01.
- n — number of months. A 20-year SIP has n = 240.
The trailing (1+i) factor is the annuity-due adjustment — it assumes you invest at the start of each month (so the money earns one extra month of compounding). This matches AMFI's standard SIP calculator convention.