Why the 5th of the month matters for PPF

PPF doesn’t calculate interest on your balance at year-end, or even at the end of each month. Every single month, interest runs on whichever balance is lower: what you had on the 5th, or what you had at any point between the 5th and the last day. For a typical account that only ever grows within a month, that rule collapses to something simple — money that lands on or before the 5th earns that month’s interest; money that lands after the 5th doesn’t start earning until the next one.

The rule: interest runs on your lowest balance, 5th to month-end

The Public Provident Fund scheme rules set the interest calculation window explicitly: each month, interest is worked out on the lowest balance in the account between the 5th and the last day of that month. Deposits are the only thing that move a typical PPF balance during the month — there’s no mid-month debit for most account holders — so the “lowest balance” in that window is effectively the balance right after the 5th, before any later deposit that same month lands.

That has a direct consequence: a deposit made on the 3rd is already sitting in the account by the 5th, so it counts toward that month’s lowest balance and earns interest starting that same month. The identical deposit made on the 7th arrives after the interest window for that month has already been measured, so it earns nothing until the following month — even though it’s only two days later.

What missing the 5th actually costs

At PPF’s current 7.1% annual rate, the monthly rate works out to about 0.592%. A single monthly instalment of ₹12,500 (the maximum ₹1,50,000 a year, spread evenly across 12 months) makes a small but real difference depending on which side of the 5th it lands.

₹74 on one instalment isn’t large by itself. But it’s not a one-time slip either — it’s a monthly habit that either helps or costs you, every single month, for as long as the account stays open.

The same rule, compounded: lump sum vs. monthly over 15 years

The same lowest-balance principle scales up into a much larger effect once you compare two full deposit strategies over PPF’s 15-year lock-in — not about missing the 5th, but about how early in the year the money starts earning in the first place. Both scenarios below deposit the maximum ₹1,50,000 every year, on time, at 7.1%; the only difference is whether it goes in as one lump sum or spread across twelve monthly instalments.

That’s a gap of ₹1,23,610over the full 15 years — without contributing a single extra rupee, purely from how early in the year the money was actually sitting in the account earning interest. The gap starts immediately: in just the first year, the lump-sum depositor earns ₹10,650 in interest against the monthly depositor’s ₹5,769, a difference of ₹4,881 before compounding has even had time to build on itself.

None of this requires depositing more than the ₹1,50,000 annual limit, and it has nothing to do with choosing a better investment — both scenarios earn the same 7.1% rate. It comes down entirely to timing: money that arrives earlier, and on the right side of the 5th, has simply had longer to earn interest before the account’s 15-year lock-in ends.