If you have ever tried to figure out manually what your PPF will be worth after 15 years, you know how tedious that math gets. A PPF calculator does it for you in seconds. Put in how much you plan to invest each year, pick your duration, and it tells you exactly what you will walk away with at maturity: no spreadsheets, no formulas, no guessing.

The math behind it is based on compound interest, but the calculator handles all of that. What you need to know is that PPF interest compounds annually — meaning every year, your interest gets added to your principal, and next year you earn interest on that larger amount too. That is what makes 15 years of consistent investing so powerful.

The formula used is F = P × [((1 + i)^n – 1) / i] — but again, the calculator runs this automatically the moment you hit calculate.

Say you put in ₹1,50,000 every year — the maximum allowed — for 15 years at the current rate of 7.1%. Here is what that looks like:

• Total amount you put in: ₹22,50,000
• Interest your money earned: ₹18,18,209
• What you actually get back: ₹40,68,209

You invested ₹22.5 lakh and got back ₹40.68 lakh. The extra ₹18 lakh is pure interest — and none of it is taxed.

PPF — Public Provident Fund — has been around since 1968. The government created it as a way for ordinary people to build savings over time with zero risk. Your money does not go into the stock market. It does not fluctuate. The interest rate is set by the government every quarter, and whatever it is, that is what you earn — guaranteed.

A few things that make it worth knowing about:

• The government backs it directly, so your principal is never at risk.
• The interest you earn is not taxed, and neither is the amount you get at maturity.
• Your PPF balance cannot be seized by creditors, even if you face financial trouble.
• You get a tax deduction on your investment under Section 80C every year.

Minimum you can put in: ₹500 per year

• Maximum: ₹1,50,000 per year
• How long it runs: 15 years
• Interest rate right now: 7.1% compounded annually
• Tax deduction: up to ₹1.5 lakh under Section 80C
• Who can open one: any resident Indian

A lot of people do not realise post offices offer PPF accounts. They do — and the terms are identical to what you get at a bank: same interest rate, same rules, same maturity period. If your nearest post office is easier to get to than a bank branch, that is a perfectly fine place to open one.

The PPF calculator above works for post office accounts the same way it works for bank accounts. The numbers will not differ.

SBI is probably the most common place people open PPF accounts in India. But here is something worth knowing — SBI does not set the PPF interest rate. The government does. So whether you open your PPF at SBI, HDFC, ICICI, or the post office, the interest rate and the maturity amount will be the same.

Use the calculator above for your SBI PPF — the result is what you will actually get.

This trips a lot of people up. PPF interest is worked out on the lowest balance sitting in your account between the 5th and the last day of each month. The interest itself only shows up in your account once a year, on March 31.

What this means practically: if you deposit money before the 5th of any month, that deposit earns interest for that whole month. Deposit it on the 6th, and you lose that month entirely. For anyone putting in a lump sum once a year, April 1 to April 5 is the window you want.

• Put money in before the 5th of each month — even one day late costs you a month of interest.
• If you invest annually, do it in the first week of April, not March — you get a full year of interest instead of a few days.
• Try to hit the ₹1.5 lakh ceiling every year — it maximises both your returns and your tax saving.
• The earlier you start, the harder compounding works for you — a 25-year-old who starts today will end up with far more than someone who waits until 35
• When your account matures, think twice before closing it — you can extend in 5-year blocks and keep the tax-free growth going.