Investing
Compound Interest Calculator
Estimate how a starting balance and steady monthly investing can grow over time through compound returns.
Model long-term portfolio growth, compare contribution habits, and see how time changes the result more than most people expect.
Investing
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Scenario presets
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Example
$500 per month for 20 years at 8% can build a portfolio much larger than your raw contributions alone.
Results
Final balance
$343,778
Total contributions
$130,000
Investment growth
$213,778
Projection
Trend view
Start now vs wait
Gap created by waiting: $121,491
Growth engine
62.2% of the projected ending balance comes from returns rather than direct deposits.
Planning cue
At the current pace, $500 per month compounds over 20 years into a materially larger outcome.
This projection assumes a steady return rate and monthly compounding.
How it works
What the result is showing you
These sections explain what the calculator measures, which assumptions matter most, and where the number can be misleading.
What is compound interest?
Compound growth means your money can earn returns on both the original balance and the gains that build up over time. The longer the timeline, the more noticeable that snowball effect becomes.
How compound interest works
This calculator applies a monthly growth rate to the current balance and then adds the recurring contribution you entered. Repeating that process over many months is what makes long-term investing look very different from simple addition.
Why starting early matters
More time in the market often does more work than trying to find a slightly higher return later. Starting earlier gives every future contribution more time to compound.
Common questions
- compound interest calculator with monthly contributions
- how much will 1000 grow in 20 years
- compound interest calculator 10 years
Frequently asked questions
Is compound interest monthly or yearly?
Compounding can happen daily, monthly, quarterly, or yearly depending on the account. Monthly compounding is a useful planning baseline because it lines up well with recurring contributions.
What is a good return rate?
Many long-term stock-heavy scenarios use something in the 6% to 10% range before inflation, but there is no guaranteed return. It is better to test conservative, middle, and optimistic scenarios than rely on one number.
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