Which Post Office scheme fits which goal
These four schemes solve different problems, not the same one at different rates. PPF is the general-purpose long-term option — anyone can open one, it's tax-free end to end, and the 15-year lock-in suits retirement-horizon savings. Sukanya Samriddhi Yojana offers the highest rate of the group but is restricted to a girl child under 10 at account opening, making it purpose-built for that specific savings goal rather than a general option. RD suits small, regular monthly savers who want a fixed, predictable commitment without a large upfront lump sum. FD (Time Deposit) suits a lump sum you want parked safely for a fixed, shorter term, with the 5-year term specifically earning a tax deduction the shorter terms don't.
All four are backed by the Government of India, which means the safety profile is essentially identical across them — the real decision points are liquidity (how long you can lock money away), whether you have a lump sum or want to save monthly, and whether the tax-free treatment of PPF/SSY is worth more to you than RD or FD's shorter commitment. Pick the calculator above that matches your actual situation rather than just comparing headline rates.