Interactive Tools

Free calculators to help you think through financial decisions. All calculations happen in your browser — nothing is sent anywhere.

Compound Interest Calculator

See how an initial investment grows over time with regular contributions. Uses monthly compounding. Read the full lesson on compound interest →

⚡ Compound Interest
Interactive
$10,000
$200
7.0%
30 years
— Total Value
— Total Contributed
— Interest Earned

For illustrative purposes only. Does not account for taxes, fees, or inflation. Returns are not guaranteed.

Emergency Fund Calculator

Most financial planners recommend keeping 3–6 months of essential living expenses in a liquid, low-risk account (such as a high-yield savings account). This calculator helps you find your target amount.

🛡 Emergency Fund
Interactive
$1,500
$400
$200
$300
— Monthly Essentials
— Target Emergency Fund

Guideline: 3 months if you have stable income/two earners; 6+ months if self-employed or in a volatile industry.

Rule of 72 — Doubling Time

The Rule of 72 gives a quick estimate of how long it takes an investment to double at a given annual rate of return. Divide 72 by the rate to get approximate years. Read the full lesson →

72 Rule of 72
Interactive
7.0%
— Approx. Years to Double (Rule of 72)
— Exact Years (log formula)

Works well for rates between 6–12%. At extreme rates, use the exact formula: t = ln(2) / ln(1 + r).

Federal Income Tax Calculator

Calculate your estimated federal income tax based on 2024 tax brackets. See how the progressive bracket system works — where only the income in each bracket is taxed at that bracket's rate. Read the full lesson on tax basics →

📊 2024 Federal Tax Calculator
Interactive
$60,000
— Taxable Income
— Total Tax
— Effective Rate
— Marginal Tax Bracket
— Take-Home After Tax

Based on 2024 federal tax brackets. Does not include state taxes, FICA, or other deductions. For educational purposes only.