Compound Interest Calculator

Core formula

A common lump-sum compound interest formula is FV = PV x (1 + r / n) ^ (n x t). FV is future value, PV is initial principal, r is annual return, n is the number of compounding periods per year, and t is the time horizon in years.

When recurring monthly contributions are included, CompoundX treats each contribution as a separate cash flow and compounds it over the remaining time horizon.

Inputs

• Initial principal: the amount invested at the start.
• Monthly contribution: the fixed amount added each month.
• Annual return: a scenario assumption, not a guaranteed future return.
• Investment period: the number of years the money remains invested.
• Compounding frequency: how often returns are added back to the balance.

Useful scenarios

Compound growth estimates are useful for long-term savings, index investing, retirement planning, education funding, and portfolio goal planning. They are best used to compare scenarios, not to predict exact outcomes.

Example

If you start with 100,000, add 3,000 each month, assume an 8% annual return, and invest for 30 years, the result will be heavily influenced by time and ongoing contributions. Real results still depend on volatility, fees, taxes, and cash-flow changes.

Important limitation

This page and calculator are for estimation only and do not constitute investment advice. Example return assumptions should not be treated as promises.