I did not add inflation to these tools as a marketing badge. I added it because the first number people screenshot - “₹99.9 lakh after 20 years” is the number that most often lies. It is true in future rupees. It is not true in the rupees you use to buy rent, fees, and hospital bills today. This page is the method note for how growwithsip turns one into the other, and where it refuses to pretend.
What the page actually computes
On the SIP calculator, the engine first compounds monthly at the expected-return slider (the ordinary future value of an annuity due). That is the nominal corpus. Separately, an inflation factor (1 + i)n is applied to that terminal value to print a real value in today’s rupees. Year-by-year rows use the same idea at each year, not only at maturity. Goal targeting inflates the goal first, then solves for the SIP that funds the inflated amount. That is why a ₹1 crore “today” goal needs a larger monthly debit than a ₹1 crore “future” goal.
I use a constant i. Markets do not. CPI in India has printed 2% and 8% in different years. Healthcare and school fees often run hotter than headline CPI. If your actual basket inflates at 8%, type 8%. Do not leave 6% because it is the default.
Fisher, not “12 minus 6”
Real return is ((1 + nominal) / (1 + inflation)) − 1. At 12% and 6% that is about 5.66%, not 6%. Over 20 years the difference is not a rounding error. The SIP page prints a table of purchasing power lost so you can see the curve, not a slogan. The retirement calculator works backwards from a lifestyle you describe in today’s rupees, then grows expenses with inflation so the corpus is sized for the year you stop working, not for 2026 prices.
What we do not do
- We do not pull live MOSPI CPI into the slider. Rates on the page are yours to type.
- We do not tax-adjust the real column. LTCG, slab-rate interest, and cess sit outside the deflator. Mixing them in one cell would look precise and be wrong.
- The FD calculator and PPF calculator show the contract or the notified rate. They do not auto-deflate. A 7% FD after 6% inflation is a real story you should do in your head or on the SIP page’s real column, not hide inside an FD maturity.
- Charts can still look “up and to the right” in nominal rupees while real value stalls. Read both.
A worked habit
Open SIP. Leave ₹10,000 a month, 12%, 20 years. Note nominal and real at 6% inflation. Move inflation to 8%. The real column collapses further; the nominal column does not care. That is the demonstration I wanted when I was reverse-engineering other sites that only advertised the crore. Then open the goal planner and set a goal you actually have a house down payment quoted in today’s asking price and let the tool inflate it. If you type the future asking price yourself, you will double-count inflation. That trap has its own note.
I am not a SEBI-registered adviser. A 6% inflation slider is a planning stub. Confirm current CPI and your own expense inflation before you treat any real corpus as a promise.