Finance tools
Compound interest calculator
Model savings and investment growth, compare two scenarios, or work backward to a monthly savings goal. Choose daily, monthly, quarterly, or annual compounding — with chart, yearly table, optional inflation, and CSV or PDF export.
What is compound interest?
Compound interest is interest calculated on your original balance plus interest you have already earned. Each compounding period, earned interest is added to the balance, so the next period earns interest on a larger amount — the classic “interest on interest” effect.
That snowball effect is why long-term saving and investing can outpace simple interest, where interest is paid only on the principal and never on prior interest.
Simple interest
$10,000 at 5% for one year → $500 interest every year on the original $10,000 only.
Compound interest
Same rate, compounded monthly → about $511 in year one, then interest grows on a rising balance each year.
Why it matters
Time + regular contributions amplify compounding — especially for retirement and long-term goals.
Who uses this calculator?
Savings goals, high-yield savings (HYSA) estimates, index-fund growth illustrations, and retirement planning math — always pre-tax and before fees unless you lower the rate manually.
Compound interest formula
Standard formula
A = P(1 + r/n)ntA = ending amount · P = principal · r = annual rate (decimal) · n = compounding periods per year · t = years
With monthly contributions, this calculator compounds each period and adds deposits at the end of each month — a common assumption for savings and brokerage accounts.
Convert the annual rate
Divide your annual percentage by 100 (5% → 0.05).
Pick compounding frequency
Set n: daily = 365, monthly = 12, quarterly = 4, annually = 1.
Apply the formula per period
Each period multiplies the balance by (1 + r/n), then adds any contribution for that period.
Worked formula example ($5,000 at 5% monthly, 1 year)
A = 5,000 × (1 + 0.05/12)12 ≈ $5,255.81 with no extra deposits — a pattern many finance sites use for snippet-friendly math.
APY vs. interest rate
Interest rate is the quoted annual rate before compounding frequency is applied. APY (annual percentage yield) includes compounding — a 5% rate compounded monthly has a slightly higher APY than 5% compounded once per year. Banks often advertise APY on savings products; this tool uses a nominal annual rate plus your chosen compounding frequency.
How much will $10,000 grow in 10 years at 5%?
A common search question — here is the math from this calculator with $10,000 initial balance, 5% annual rate, 10 years, and monthly compounding (no extra contributions):
Add $200/month at 5% for 20 years → about $109,333 ending balance ($58,000 contributed). Try the $10k + $200/mo · 20y · 7% preset for a higher-return long-term scenario (~$144,573).
Daily compound interest calculator (HYSA example)
Many high-yield savings accounts compound daily. Select Daily compounding in the calculator above — the same pattern top US finance publishers use in worked examples.
$10,000 at 4% APY-style rate, daily, 10 years
With no further deposits: ending balance ≈ $14,917.92 and interest earned ≈ $4,917.92. Rates change; use your account’s current yield and compounding rules.
Related queries like monthly compound interest calculator or yearly compound interest calculator map directly to the compounding dropdown — no separate tool required.
Compound interest for retirement and long-term goals
Retirement searches often ask how a lump sum grows over 20–30 years. Investment returns vary year to year; long-term illustrations often use average annual return assumptions (not a guarantee).
$10,000 · 7% · 30 years · monthly
No further contributions → about $81,165 (illustrative).
$150/month · 7% · 30 years
Starting from $0 → use Growth mode; ending balance depends on start balance and rate.
Savings goal mode
Target $100,000 in 20 years at 6% with $10,000 saved → about $144.79/month required.
Not a retirement plan
This calculator does not model 401(k) limits, employer match, RMDs, or tax-advantaged accounts. Use it for math checks; consult a fiduciary advisor for personal retirement planning.
How compounding frequency affects growth
More compounding periods per year mean slightly higher growth at the same nominal annual rate. This tool supports daily, monthly, quarterly, and annual compounding — aligned with related SERP variants (daily / monthly / yearly calculators).
| Frequency | Typical use | Effect at same nominal rate |
|---|---|---|
| Daily | HYSA, some money-market accounts | Highest ending balance |
| Monthly | Brokerage auto-invest, many projections | Common long-term default |
| Quarterly | Some CDs, legacy products | Slightly below monthly |
| Annually | Simple teaching examples | Lowest ending balance |
Compare scenarios and savings goals
Compare mode runs Scenario A and B side by side — useful when you want to test a higher monthly contribution vs. a longer timeline without switching browser tabs.
Savings goal mode solves backward: enter your target balance and see the monthly contribution required at your rate and timeline.
Limitations (v1)
No withdrawal or loan amortization engine, no US capital-gains tax modeling, and no weekly contribution cadence. Optional inflation shows a simplified real balance — not a tax or fee estimate. Educational reference: Investor.gov compound interest calculator.
For quick percent math (discounts, shares, percent change), use the percentage calculator or browse more free calculators.
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Frequently asked questions about this compound interest calculator
How do you calculate compound interest?
Enter initial balance, optional monthly contribution, annual interest rate, years, and compounding frequency. The calculator applies the compound formula each period and shows ending balance, total interest, and a yearly breakdown chart and table.
What is the compound interest formula?
A = P(1 + r/n)nt — P is principal, r is the annual rate as a decimal, n is compounding periods per year, and t is time in years. Monthly contributions are added at the end of each month.
How much will $10,000 grow in 10 years at 5%?
With monthly compounding and no extra deposits: ending balance ≈ $16,470.09 (interest ≈ $6,470.09). Enter $10,000, 5%, 10 years, and monthly compounding in Growth mode for the exact figure.
How does a daily compound interest calculator work?
Choose Daily compounding. The annual rate is split across 365 periods per year (with monthly deposits handled in sub-periods). Example: $10,000 at 4% daily for 10 years with no contributions → about $14,917.92 — typical for HYSA illustrations.
What is the difference between APY and interest rate?
Interest rate is the quoted annual rate before compounding. APY reflects how often interest compounds — higher frequency raises APY slightly at the same nominal rate. This tool uses a nominal annual rate plus your selected compounding frequency.
Can I use this compound interest calculator for retirement?
Yes for illustrative long-horizon math (e.g. 30 years at an assumed average return). It does not model 401(k) rules, taxes, or fees. Lower the rate manually to approximate costs, or use Savings goal mode to back-solve monthly contributions.
What is simple interest vs compound interest?
Simple interest is paid only on the original principal. Compound interest is paid on principal plus accumulated interest, so balances accelerate over time — especially with monthly contributions.
How much do I need to save each month to reach my goal?
Use Savings goal mode: enter your target balance, rate, years, and starting amount. Example: $100,000 in 20 years at 6% with $10,000 saved → about $144.79/month.
Does this calculator include withdrawals or taxes?
No. Withdrawals and US capital-gains tax are not modeled in v1. Results are pre-tax. Optional inflation adjustment shows a simplified purchasing-power estimate — not tax advice.
Can I export my results?
Yes — download CSV or PDF with inputs, summary totals, and the yearly breakdown. Free, no account required.