Compound Interest Calculator
Calculate investment returns, compound growth, and portfolio performance.
Enhanced with Universal System!
Advanced financial planning with milestone tracking and scenario analysis
Calculator Tools
Quick Actions
Enhanced Compound Interest Calculator
Plan your financial future with advanced compound interest calculations, scenario comparisons, and milestone tracking
How it works
Compound interest pays interest on your interest. Each period, the rate is applied to the whole balance — including the interest already earned — so growth accelerates over time. The more often interest compounds (yearly, monthly, daily) and the longer it runs, the bigger the gap between what you put in and what you end up with.
Compound interest (lump sum)
A = P · (1 + r/m)^(m · t)
- A
- final amount (balance at the end)
- P
- principal (starting amount)
- r
- annual interest rate (as a decimal)
- m
- times interest compounds per year
- t
- number of years
Worked example
- Principal P = $10,000
- Rate r = 7% = 0.07, compounded monthly (m = 12)
- Time t = 10 years
- A = 10,000 × (1 + 0.07/12)^(12 × 10)
- A = 10,000 × 1.005833¹²⁰ ≈ 10,000 × 2.01
Final balance ≈ $20,097 — your money roughly doubles in 10 years at 7%.
Good to know
- Rule of 72: divide 72 by the rate to estimate the doubling time — at 7%, that's ~10.3 years, matching the example.
- Higher compounding frequency helps, but only a little: daily vs annual at 7% over 10 years differs by well under 1%.
- Adding regular contributions changes the math — each deposit is its own compounding stream, which is why monthly investing outpaces a single lump sum over long horizons.
- These figures are before inflation and taxes; a 7% nominal return is closer to ~4% in real purchasing power.
Can't find the exact calculator you need?
Describe it in one sentence — get a working, math-verified calculator in seconds. Free, no signup.
Build your own calculatorRelated Calculators
Frequently Asked Questions
How does compound interest work?
Compound interest is earning interest on both your principal and previously earned interest. The longer you invest, the more powerful compounding becomes.
How often should I review my investments?
Review quarterly but avoid daily monitoring. Rebalance annually or when allocations drift 5-10% from targets. Stay focused on long-term goals.
What's the Rule of 72?
The Rule of 72 estimates how long it takes to double your money. Divide 72 by your annual return rate. At 8% return, your money doubles in about 9 years (72÷8=9).
How does compounding frequency affect returns?
More frequent compounding yields higher returns. Daily compounding beats monthly by about 0.1-0.2% annually. The difference is larger with higher interest rates.
Should I invest a lump sum or make regular contributions?
Both have benefits. Lump sum investing gets more time in the market. Dollar-cost averaging through regular contributions reduces timing risk and builds discipline.
What's a realistic long-term investment return?
Historically, stock markets average 7-10% annually over 20+ years. Bonds average 3-5%. A balanced portfolio typically returns 6-8% before inflation.