How this calculator works
Each deposit is made in April and then at equal monthly intervals for the selected frequency. Deposits on or before the fifth qualify for that month's interest; later deposits first qualify the next month. Interest is summed monthly and added after each financial year. Annual deposits are checked against INR 500 and INR 150,000. The projection models 15 full financial years and five-year extensions with no withdrawals. Legal maturity is measured from the end of the opening financial year, so this full-year projection is not an exact account-opening maturity quote. Future government rates can change.
Formula
Monthly interest = eligible monthly balance x annual rate/12. Financial-year closing balance = opening balance + deposits + sum of monthly interest. Required deposit = target/unit-deposit projected balance.
Worked example
An INR 1,000 deposit before 5 April at 10% earns INR 100 during the first full financial year. Depositing after 5 April earns interest for 11 months, or INR 91.67. At 0%, INR 1,000 annually for 15 years totals INR 15,000.
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Frequently asked questions
Why does the fifth day matter?
Interest uses the lowest balance between the close of the fifth day and the end of the month.
Are future PPF rates fixed?
No. A constant user-entered rate is used for the whole projection; notified rates may change.
Does this reproduce an existing passbook?
No. It assumes a new full-year saving schedule without withdrawals, irregular dates or earlier balances.