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📈 Compound Interest Calculator

Every growth scenario,
one calculator

Contributions, step-up, lump sums, inflation, tax, fees, APY, Rule of 72, goal seek, and scenario comparison — all instant, all in your browser.

1. Starting Amount, Rate & Term

2. Regular Contributions

Optional — add a recurring deposit on top of your starting amount.

Increases your contribution every 12 months

3. One-Time Lump Sum Additions

Optional — add extra deposits at specific years (e.g. a bonus in year 5).

4. Advanced Adjustments

Optional — model inflation, taxes, and account fees.

🎯 Goal Seek

Work backward from a target amount using your other current settings.

⚖️ Compare Scenarios

Save up to 3 calculated scenarios side by side using "💾 Save as Scenario" above.

🕘 Local History

Saved only on this device — never uploaded anywhere. Click an entry to reload it.

No history yet — calculate above to see it appear here.
How To

How to use every option

  1. Enter your starting amount, rate, and term — the principal you're starting with, the annual interest rate, and how many years (plus extra months) you're projecting.
  2. Pick a compounding frequency — Annually, Semi-Annually, Quarterly, Monthly, Bi-Weekly, Weekly, Daily, or Continuous. More frequent compounding slightly increases your effective return.
  3. Choose a currency for all displayed amounts.
  4. Add regular contributions (optional) — set an amount, a frequency (monthly/quarterly/annually), and whether deposits happen at the start or end of each period. Use Annual Step-Up to simulate contributions that grow every year, like redirecting a raise into savings.
  5. Add one-time lump sums (optional) — click "＋ Add Lump Sum" for each extra deposit, entering the year it happens and the amount (e.g. a bonus in year 5).
  6. Set advanced adjustments (optional) — an inflation rate to see your real, inflation-adjusted future value; a tax rate applied to interest earned; and an annual fee/expense ratio deducted from the balance.
  7. Click Calculate to see your Future Value, total contributed, total interest, total fees, Effective Annual Rate (APY), Rule of 72 doubling time, real value, and post-tax value.
  8. Review the growth chart — a stacked area chart showing contributions versus interest earned over time.
  9. Check the year-by-year table — opening balance, contributions, interest, fees, and closing balance for every year, downloadable as CSV.
  10. Use the sensitivity table to see how a ±1–2% rate change would affect your result.
  11. Try Goal Seek — enter a target amount and solve for the rate, contribution, or time needed to reach it, based on your other current settings.
  12. Save and compare scenarios — save up to 3 calculated results side by side to compare different strategies.
  13. Copy, print, or share — copy a plain-text summary, print a report, or copy a shareable link that pre-fills your core inputs for someone else.
  14. Revisit past calculations from Local History, or clear it whenever you like.
Capabilities

Built to replace a dozen separate calculators

🔁
8 Compounding Frequencies
From annually to continuous compounding, including bi-weekly and daily.
📈
Step-Up Contributions
Model annually increasing deposits, not just a flat recurring amount.
💰
One-Time Lump Sums
Add bonuses or windfalls at any year alongside regular contributions.
🌍
Inflation & Tax Adjustment
See both the real (inflation-adjusted) and post-tax future value.
📊
APY & Rule of 72
Effective annual rate and a quick doubling-time estimate, shown automatically.
🎯
3-Way Goal Seek
Solve for the required rate, contribution, or time to hit any target.
⚖️
Scenario Comparison
Save and compare up to 3 calculated strategies side by side.
📉
Growth Chart & CSV
A visual breakdown chart plus a full downloadable year-by-year schedule.
🔒
100% Private
Every calculation stays in your browser — nothing is ever uploaded.

Frequently Asked Questions

Interest is calculated on the current balance at each compounding period, then added back to the balance so future interest is earned on both the original amount and prior interest. This calculator also layers in any regular contributions, lump sums, and fees on their own schedules.

The nominal (annual) rate is the stated yearly rate before compounding is applied. The Effective Annual Rate, or APY, is the true yearly return once compounding frequency is factored in, and is always equal to or higher than the nominal rate.

Dividing 72 by the annual interest rate gives a quick estimate of how many years it takes an investment to double, assuming no additional contributions. It's an approximation, not an exact calculation.

The real value divides the projected future value by the cumulative effect of your entered inflation rate over the same time period, showing what that future amount would be worth in today's purchasing power.

The post-tax value applies your entered tax rate to the total interest earned only (not to contributions), then adds that after-tax interest back to your contributions. This is a simplified estimate — real-world tax treatment depends on your account type and jurisdiction.

Yes. Set an annual step-up percentage and your regular contribution amount will automatically increase by that percentage every 12 months, similar to redirecting an annual raise into savings.

Goal Seek works backward from a target amount to tell you the annual rate, the contribution amount, or the time needed to reach it, using the other values you've already entered.

No. Every calculation, chart, and export runs locally in your browser. Local history and saved scenarios are stored only in this browser's local storage on your device.

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