Investments • Compound growth
Compound Interest Calculator
Estimate future value from a starting amount and optional monthly contributions. Test several rates rather than treating one smooth projection as a promise.
Enter growth assumptions
How to use it
- Enter current savings, or zero when starting only with monthly deposits.
- Add an optional monthly contribution.
- Enter an illustrative annual rate and duration.
- Select how often the nominal annual rate compounds.
- Compare lower, middle and higher scenarios.
Formula and methodology
AP = P(1 + r/k)kt
AM = M × [((1 + i)n − 1) ÷ i] × (1 + i)
P is principal, r is annual nominal rate, k is compounding periods, t is years, M is monthly contribution, n is months and i is the equivalent monthly rate. Total value is AP + AM. Values are rounded to the nearest rupee.
Worked Indian example
Starting with ₹1,00,000, adding ₹5,000 per month for 10 years, and assuming 10% compounded monthly gives:
| Total contributions | ₹7,00,000 |
|---|---|
| Estimated growth | ₹6,03,464 |
| Estimated total value | ₹13,03,464 |
A steady 10% outcome is illustrative. Real products may deliver uneven returns and incur tax or costs.
Reading the result
Total contributions are the cash added. Growth is the mathematical difference between projected value and contributions. It is not guaranteed interest unless the underlying product itself offers a contractual rate.
Common mistakes
- Using a recent high return as a permanent forecast.
- Ignoring inflation, tax and fees.
- Mixing annual and monthly rates.
- Assuming frequent compounding removes investment risk.
Practical tips
- Start with a conservative scenario.
- Use a contribution you can maintain.
- Match product risk to goal duration.
- Keep short-term needs outside volatile investments.
- Review progress using actual values, not only forecasts.
Related calculators and guides
Frequently asked questions
What is compound interest?
Growth on principal and accumulated growth.
Are monthly contributions included?
Yes, as optional beginning-of-month contributions.
Is the return guaranteed?
No.
What does frequency change?
How often the nominal annual rate applies.
Are tax and fees included?
No.
Can principal be zero?
Yes, if monthly contribution is positive.
Why does time matter?
Accumulated growth has more time to compound.
Is this the same as CAGR?
No. CAGR measures annualized change between two values.
Educational disclaimer
This calculator is for general education, not personalized investment or tax advice. Market-linked returns are not guaranteed, and actual outcomes can be lower than contributions.