How this calculator works
- Step 1Invest onceone depositBuy the certificate at the rate in force.
- Step 2Grows yearly7.5% a yearInterest compounds once a year.
- Step 3Doubles115 monthsThe deposit is paid back twice over.
A Kisan Vikas Patra (KVP) doubles your deposit. The rate decides how long that takes: India Post says 7.5% doubles it in 115 months, which is 9 years and 7 months.
Enter the amount and the rate printed on your certificate. The calculator shows the maturity value and the doubling term. For any rate other than the current one, the term is an estimate from the formula below.
Worked example: ₹1 lakh
- Doubling time
12 × ln 2 ÷ ln(1 + rate) months
- Doubling time12 × 0.6931 ÷ ln 1.075115.01 months
- Notified term115 months (9 years 7 months)
- Maturity value2 × ₹1,00,000₹2,00,000
The formula gives 115.01 months, and India Post rounds this to a whole 115 months. Whatever you invest, the payout is twice the deposit, before tax.
Check it in your head: the Rule of 72
72 ÷ 7.5 = 9.6 years, or 115.20 months: within a month of the notified 115.
Divide 72 by the yearly rate to get roughly how many years money takes to double with yearly compounding. It is a quick sense check, not the official term.
The shortcut works best near 8%. Below that it runs slightly long, and above it slightly short. The compound interest calculator shows exact growth for any amount, rate and period.
Rate and term
A higher rate shortens the term; the payout is always double the deposit.
The rate is fixed when you buy the certificate. A later change to the notified rate does not alter an existing KVP, so an older certificate can have a different term from a new one.
KVP, NSC and PPF on the same basis
- KVP7.5% a yearAbout 115 months to double
- NSC7.7% a yearAbout 112 months to double
- PPF7.1% a yearAbout 121 months to double
All three post office schemes compound yearly, so their rates compare directly. A higher rate is not the whole story: how long the money is locked in, and how the return is taxed, matter as much.
Work through each scheme in the NSC calculator and the PPF calculator. To compare with a bank deposit, use the FD calculator, which handles quarterly compounding and payouts.
Reading the result
- Maturity valueTwice the deposit, paid in one go.
- TermMonths until that payout is due.
- RateThe yearly rate the term implies.
- Before taxWhat you keep depends on your tax.
A doubled amount buys less in 9 years than it does today. The inflation calculator shows what a future sum is worth in today’s money.
Assumptions and limits
- Held to maturityEarly encashment is not modelled.
- Fixed at purchaseLater rate changes do not apply.
- Before taxTax treatment is not included.
- Other ratesTerms for other rates are estimates.
The calculator does not check scheme rules such as minimum deposits or who may open a certificate. Confirm these at a post office or on the India Post website before you invest.
Common mistakes
Mistake: Using today’s term for an old certificate.
Instead: Enter the rate printed on it.
Mistake: Expecting yearly interest payouts.
Instead: KVP pays once, at maturity.
Mistake: Reading the doubling as tax-free.
Instead: Check how the gain is taxed for you.
Mistake: Comparing rates with different compounding.
Instead: Compare yearly rates on the same basis.
Checking the method
A separate script finds each doubling month by stepping month by month, and reproduces India Post's 115 months at 7.5%.
The independent check never uses the logarithm formula. It steps through the months until the balance first reaches twice the deposit, and agrees with the calculator at every tested rate. See how we test our calculators, or browse more money calculators.