Compound Interest Calculator

What Real Savings Actually Look Like

A lump sum growing alone is the textbook example, but most real savings scenarios involve regular deposits on top of a starting amount. This tool models exactly that — any compounding frequency, plus a monthly contribution — and visualizes how much of your final balance is money you put in versus interest that compounded on its own.

How to Use This Tool

1. 1Enter your initial investmentA lump sum you're starting with — can be zero.
2. 2Add a monthly contributionWhat most real savings actually look like — regular deposits on top of a starting amount.
3. 3Set the return rate, time period, and compounding frequencyDaily, monthly, quarterly, or yearly compounding.
4. 4Read the growth chartSee exactly how much of your final balance is money you put in vs. interest you earned.

Good to Know

• Contributions are modeled monthly — the common real-world case — while the compounding frequency you choose still affects how interest itself accrues.
• A higher compounding frequency (daily vs. yearly) makes a small but real difference to your final total, even at the same nominal annual rate.
• The chart splits your final balance into what you actually contributed vs. what interest alone added — often a bigger share than people expect over long periods.
• This models growth, not any specific investment product — actual returns from real investments vary and aren't guaranteed.

Frequently Asked Questions