What the PPF calculator projects
The PPF calculator estimates your account's maturity value at the end of its term, based on how much you contribute each year, the interest rate applied, and how many years the account runs for — including any extensions beyond the mandatory 15-year lock-in.
Unlike a SIP calculator, which deals with monthly contributions compounding at slightly different points, PPF interest is calculated on the lowest balance in your account between the 5th and last day of each month, then credited once a year, on 31 March. The calculator simplifies this by assuming your full yearly contribution goes in at the start of the year, so the entire deposit earns interest for the whole year — which is also the single most effective way to actually use a real PPF account, not just how the calculator models it.
Why the deposit date matters more than people realise
Because PPF interest is calculated on the lowest monthly balance, depositing your full year's contribution on 1 April, right at the start of the financial year, earns you a full year of interest on that money. Depositing the same amount on 31 March instead, right before the year closes, earns you close to nothing for that year.
Most people either forget and deposit late in the year, or spread contributions across 12 monthly instalments out of habit. Both approaches earn less interest over the account's lifetime than a single lump sum deposited on day one of the financial year — the calculator's projection assumes you're doing the latter, so if your actual deposit habit is different, your real maturity value will come in somewhat lower than what the tool shows.
To put a number on it: on a ₹1,50,000 yearly contribution at 7.1%, depositing on 1 April versus spreading it monthly across the year costs you roughly ₹5,000–6,000 in lost interest in that single year alone — and that gap compounds every year it repeats across a 15-year term.
How to read the year-by-year table
Below the headline maturity figure, the calculator shows a year-by-year breakdown of your deposit, interest earned that year, and closing balance. Two things are worth noticing in this table: first, the interest earned grows every year even at a constant contribution amount and rate, because it's compounding on an ever-larger balance. Second, the gap between your total invested and your closing balance widens sharply in the later years — this is the part of compounding that's easy to underestimate when you're only 3 or 4 years into an account and the numbers still look modest.
On a full ₹1,50,000 yearly contribution at 7.1% over 15 years, total invested comes to ₹22.5 lakh, but the maturity value lands closer to ₹40.7 lakh — meaning interest alone contributes more than your actual deposits by the time the account matures.
The 15-year lock-in, and what happens after
A PPF account has a mandatory 15-year term from the date of opening, not from your first deposit, and you generally cannot withdraw the full balance before that — though partial withdrawals are allowed from the 7th year onward under specific conditions.
When the 15 years are up, you have three choices: withdraw the entire maturity amount and close the account, extend the account in blocks of 5 years while continuing to contribute, or extend it in blocks of 5 years without any further contributions, where the existing balance simply keeps earning interest. The calculator's tenure selector (15/20/25/30 years) lets you model the second option — continuing to contribute through one or more 5-year extensions — which is usually the choice that produces the largest final corpus if you don't need the money at the 15-year mark.
Extending without further contributions is worth understanding too, since it's a genuinely useful option if your income situation changes: your existing balance keeps compounding at the prevailing PPF rate with zero new money required, which effectively turns a maturing PPF account into a passive, government-backed holding you can leave untouched for as long as you want, in 5-year blocks.
PPF versus other 80C options, briefly
PPF sits inside the broader 80C basket alongside options like ELSS mutual funds, EPF, and life insurance premiums, all competing for the same ₹1.5 lakh annual deduction limit. What sets PPF apart is the combination of a government-backed guarantee and complete tax exemption on the way out, at the cost of a long lock-in and a rate that moves with government policy rather than the market.
If you're deciding how to split your 80C allocation, it's worth thinking about PPF less as an investment competing on returns, and more as the fixed-income, zero-risk portion of your portfolio — with growth-oriented 80C options like ELSS handling the higher-risk, higher-potential-return side. A common approach is to fill PPF up to a level that covers a genuinely risk-free portion of your retirement goal, and direct the remaining 80C headroom toward ELSS or NPS for growth.
It's also worth weighing lock-in periods side by side: ELSS has just a 3-year lock-in, EPF is generally accessible at retirement or after a continuous employment gap, while PPF's 15-year term is the longest of the three. That long horizon is exactly why PPF suits money you're confident you won't need for well over a decade — treating it as a substitute for an emergency fund or medium-term goal defeats its purpose.
Common mistakes when using a PPF calculator
Assuming the current interest rate holds for the full term. A 15–30 year projection at today's rate is a starting estimate, not a promise — the actual rate will almost certainly move several times over that period, both up and down, depending on broader interest rate cycles.
Forgetting the ₹1.5 lakh annual contribution ceiling. That's the maximum PPF deposit allowed per financial year across all your PPF accounts combined, including any account opened for a minor child under your guardianship; anything modeled above that in a calculator isn't realistic.
Not modelling extensions correctly. If you plan to extend past 15 years, be clear with yourself about whether you'll keep contributing or let the balance sit — these produce very different outcomes, and the calculator's tenure toggle only reflects the with-contribution scenario, not the passive extension option.