Methodology and assumptions
How CompoundCalc Calculates Compound Interest
Every calculator on CompoundCalc is an educational estimate. This page explains the formulas, assumptions and limits so users can judge the result instead of treating it as financial advice.
Core formula
Future value = principal × (1 + annual rate / compounding periods) ^ (compounding periods × years)
This formula works for a single starting amount. Pages with monthly contributions add each deposit into the projection and compound it for the remaining time.
Contribution assumptions
- Monthly contributions: most tools assume a fixed monthly deposit.
- Timing: unless stated otherwise, deposits are treated as end-of-period contributions.
- Return: the annual return is constant in the calculator, even though real markets are not.
- Currency: results use the entered number format and are not tied to a specific tax system.
What the calculators do not include
Taxes and fees
No calculator here automatically applies income tax, capital gains tax, account fees or platform charges.
Market volatility
A constant return smooths the path. Real investment returns move up and down.
Inflation surprises
Use a lower real return assumption or the inflation-related guides for more conservative planning.
Personal suitability
The site does not recommend investments or tell you what to buy.