Methodology
We show our working so you can trust the numbers — and check them.
For an annual expected return r, we use the geometric monthly rate:
Many calculators use the simpler r / 12. That shortcut compounds to more than the stated annual return over a year and inflates the maturity figure. We deliberately use the correct geometric rate, which is why our headline number is usually a little lower than other tools — and more accurate.
We iterate month by month rather than use a closed-form annuity formula, so step-ups, contribution frequency and (in the XIRR tool) irregular flows all compound correctly:
For equity funds we apply the 2024–25 long-term capital gains regime: 12.5% on gains above ₹1,25,000 per financial year. The calculators show the tax deducted as its own line so nothing is hidden. Debt-fund and short-term treatment differ; where relevant the tool notes its assumption.
Real value discounts the post-tax corpus back to today's purchasing power:
Given a target, we bisection-search the base monthly SIP whose post-tax projection equals the target (post-tax corpus is monotonic in contribution, so bisection converges quickly). If you mark the target as "today's money", we first inflate it to its future nominal value.
XIRR is the rate that sets the net present value of all dated cashflows to zero. We solve it with Newton–Raphson and fall back to bisection over a wide bracket when Newton diverges (irregular flows can cause that), using an actual/365 day count.