More in Debt & Purchase
What this calculator does
This calculator shows how compound interest grows a balance over time. Use the slider to see how the timeline changes.
The math
Each month: balance = (balance + monthly addition) × (1 + annual rate ÷ 12 ÷ 100). The loop repeats for the chosen number of years.
Worked example
Starting with $1,000, adding $200 per month, and earning 7% annually, the balance reaches about $37,000 after 10 years.
Why this matters
Most people underestimate the cost of small interest and fee decisions. This calculator turns the hidden math into a number you can act on today.
Methodology and transparency
This page publishes the exact formula used to compute the result, so you can verify it in a spreadsheet or check the assumptions against your own situation. The worked example uses the tool default inputs; change any number and the result updates live in your browser. No data is sent or stored.
Common questions
What does the slider do?
It updates the chart in real time as you change the number of years.
Is this monthly compounding?
Yes. The calculator assumes monthly contributions and monthly compounding.
How does this apply to investing?
Use the annual return as your expected average market return. The graph shows the power of consistent contributions over time.