Compound interest calculator (with contributions)
Compound interest is the process by which earnings on an investment generate their own earnings. The standard formula is FV = P × (1 + r/n)^(nt), where P is principal, r is the annual rate, n the compounding frequency and t the time in years. Adding regular contributions extends this with the future value of an annuity. This calculator handles both at once.
How to use
- Enter starting principal
Lump sum invested today.
- Enter monthly contribution
Recurring deposit added at the end of every month.
- Pick rate and horizon
Annual return and number of years.
- Read the result
Drogo returns final value, total contributions and total interest.
Frequently asked questions
- What rate of return should I assume?
- Long-run inflation-adjusted equity returns have averaged ~7% in the US since 1928, and ~5% globally. Use 5–7% as a conservative real-return assumption; never use the last 5 years of a bull market as your base case.
- Does this account for taxes?
- No — this calculator is pre-tax. Multiply by (1 − your effective dividend / capital gains rate) for an after-tax estimate, or use a tax-advantaged account.
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