How the doubling tenure is computed
Using compound interest annually: months ≈ 12 × log(2) / log(1 + r/100)
At common rates: 7.5% → 115 months; 7% → 124 months; 8% → 108 months. India Post rounds to the nearest month.
Other notes
- No upper limit on investment (KYC required for ≥₹50,000)
- Premature encashment allowed after 2 years 6 months
- Can be transferred between holders / post offices
- Interest is taxable; no TDS at maturity but interest accrued each year is income