Compound Interest Calculator
Calculate compound interest with monthly or annual compounding. See how investments grow over time.
About this calculator
This compound interest calculator is built for rupee savers. Enter a lump sum, a rate, a time and how often interest compounds, and it returns the final amount, the interest earned and the doubling time. If you also invest every month, add the monthly SIP amount and the tool folds that in as well.
It suits fixed deposits, recurring-style savings, PPF-like products and any investment where you want a quick, honest projection. The doubling time tells you at a glance how long your money takes to double at that rate.
How to use it
- Enter the Principal in rupees.
- Enter the Annual Rate and the Time in years.
- Choose the Compounding frequency: annual, quarterly, monthly or daily.
- Optionally enter a Monthly SIP to add regular contributions.
- Read the final amount, interest earned and doubling time as they update.
How the amount is worked out
Lump sum: A = P(1 + r/n)nt. SIP: FV = S × [((1 + r/12)12t − 1) ÷ (r/12)]. The doubling time shown is ln 2 ÷ (n × ln(1 + r/n)). The SIP is assumed to be invested monthly at the same rate as the lump sum.
Worked example
₹1,00,000 at 8% for 10 years with ₹5,000 a month, compounded monthly
| Lump sum grows to | ₹2,21,964 |
| Monthly SIP grows to | ₹9,14,730 |
| Final amount | ₹11,36,694 |
| Interest earned | ₹4,36,694 |
| Doubling time | 8.7 years |
Your own money is ₹7,00,000 (₹1,00,000 plus ₹6,00,000 of SIPs). The remaining ₹4,36,694 is interest.
Tips and common mistakes
- Match the compounding option to your product. Bank FDs usually compound quarterly, PPF yearly.
- Use the doubling time to sanity-check a rate: 72 divided by the rate is a good rule of thumb.
- Leave the SIP blank for a pure lump-sum projection.
- Pre-tax and post-tax results differ. Interest on deposits is taxable at your slab rate.
- Inflation erodes the real value. At 6% inflation, ₹11.4 lakh in 10 years buys what about ₹6.3 lakh does today.
Frequently asked questions
What compounding frequency should I choose?
Choose the one your product uses. Most Indian bank FDs compound quarterly, savings accounts compound daily or quarterly, and PPF compounds annually.
What is doubling time?
It is how long the money takes to double at the given rate and compounding. At 8% it is about 8.7 years with monthly compounding.
Does the monthly SIP earn the same rate?
Yes. The tool applies the same annual rate to the SIP as to the lump sum.
Is interest on the SIP also compounded?
Yes, each monthly instalment compounds from the month it is invested.
Why does the result differ slightly from my bank?
Banks round, use day counts and sometimes compound on different dates. Expect small differences.
Can I enter a negative rate?
The tool is meant for positive growth rates. Use the CAGR calculator to measure a decline.