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//// Financial · Student Tool

Compound Interest Visualizer

Watch your money grow year by year with an interactive chart. See the gap between saving and investing. Change any number — see the math update instantly.

Where this fits

📈 Investing & WealthEmployeesStudents

This tool sits in the investing & wealth domain and connects best with the next tools in that decision lane.

401(k) Limit 2024$23,000
Roth IRA Limit$7,000
S&P 500 Avg Return~10%/yr

Try a preset scenario

Your Numbers

Starting amount$100
$0$10,000

Even $0 works — try starting with nothing and just contributing monthly

Monthly contribution$50/mo
$0/mo$1000/mo

What can you realistically save each month?

Annual interest rate7%
1%15%

US stock market has averaged ~7-10% historically. Savings accounts: 4-5% today.

How many years10 yrs
1 yrs40 yrs

Time is your biggest advantage when you're young

Compounding frequency

Your money over time

With 7% interestJust saving (no interest)

Final balance

$8.9k

after 10 years

You put in

$6.1k

your actual contributions

Interest earned

$2.8k

money your money made

72

Rule of 72: at 7%, your money doubles every 10.3 years

Divide 72 by your interest rate to estimate the doubling time. At 7%, that's every ~10 years. Start at 20, and your money could double 4 times before you retire.

1

Your starting money

principal = your starting amount

= $100

This is the seed. Even a small amount, invested early, grows surprisingly large.

2

What you add each month

annualContributions = monthlyContribution × 12

= $50 × 12

= $600/year

Consistent contributions are the most powerful force in building wealth — more powerful than the interest rate.

3

Your monthly interest rate

monthlyRate = annualRate / 12

= 7% / 12

= 0.5833% per month

Banks and investments quote annual rates, but compounding happens every period.

4

Compound interest formula

A = P(1 + r/n)^(nt) + PMT × ((1 + r/n)^(nt) − 1) / (r/n)

= — the core equation

Each period, your interest earns interest too. That's the magic of compounding.

5

Balance after 10 years

balance after 10 years of compounding

= $8,855

6

Total you put in

totalContributed = principal + monthlyContribution × 12 × years

= $100 + $50 × 12 × 10

= $6,100

7

Interest earned (the wow number)

totalInterest = finalBalance − totalContributed

= $8,855 − $6,100

= $2,755 in interest — money your money made

This is money you never worked for. It was generated by the interest on your interest.

8

Rule of 72 — doubling time

doublingTime = 72 / annualRate

= 72 / 7%

= ~10.3 years to double

The Rule of 72 is a shortcut. At 7%, your money doubles every 10.3 years. At 10%, every 7.2 years.

Key insight

The secret is that interest earns interest. That's it. Start early, stay consistent, and let time do the heavy lifting.

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