A worked example: ₹40,00,000 extended 5 years, with contributions
A PPF account with a ₹40,00,000 balance at 15-year maturity, extended 5 years with continued ₹1,50,000 annual contributions, grows to ₹65,62,173.33 — made up of ₹7,50,000 in new contributions (₹1,50,000 × 5 years) and ₹18,12,173.33 in total interest earned across both the existing balance and the new deposits.
The formula: two compounding streams, added together
The existing ₹40,00,000 balance compounds on its own for the full extension period, just like any lump sum earning interest. Separately, each year's new contribution starts compounding from the moment it's deposited — so the first year's contribution compounds for nearly the full 5 years, while the last year's barely compounds at all. Adding both streams together gives the extended maturity amount.
The simpler case: extending without further contributions
The same ₹40,00,000 balance extended for 5 years without any further contributions grows to ₹56,36,471.89 — all of it interest (₹16,36,471.89), since there's only the one compounding stream from the original balance. No Form H filing is needed for this option, and one withdrawal per year is still permitted.
Why filing Form H matters if you want to keep contributing
Continuing to contribute during an extension isn't automatic — Form H must be filed at the PPF branch within 1 year of the account's original maturity date. Missing that window doesn't close the account; it just locks it into the without-contributions path, where the existing balance keeps earning interest but no further deposits are accepted.
This can repeat indefinitely
There's no limit on how many 5-year blocks a PPF account can be extended for, and each new block can independently choose to continue contributing or not — the extended maturity amount from one block simply becomes the starting balance for the next.