See how your money grows over time with regular contributions, inflation adjustment, multi-scenario comparison, and growth charts.
| Year | Balance | Contributions | Interest |
|---|---|---|---|
| 1 | $16919 | $16000 | +$919 |
| 2 | $24339 | $22000 | +$2339 |
| 3 | $32294 | $28000 | +$4294 |
| 4 | $40825 | $34000 | +$6825 |
| 5 | $49973 | $40000 | +$9973 |
| 6 | $59782 | $46000 | +$13782 |
| 7 | $70299 | $52000 | +$18299 |
| 8 | $81578 | $58000 | +$23578 |
| 9 | $93671 | $64000 | +$29671 |
| 10 | $106639 | $70000 | +$36639 |
| 11 | $120544 | $76000 | +$44544 |
| 12 | $135455 | $82000 | +$53455 |
| 13 | $151443 | $88000 | +$63443 |
| 14 | $168587 | $94000 | +$74587 |
| 15 | $186971 | $100000 | +$86971 |
| 16 | $206683 | $106000 | +$100683 |
| 17 | $227820 | $112000 | +$115820 |
| 18 | $250486 | $118000 | +$132486 |
| 19 | $274790 | $124000 | +$150790 |
| 20 | $300851 | $130000 | +$170851 |
| 21 | $328796 | $136000 | +$192796 |
| 22 | $358760 | $142000 | +$216760 |
| 23 | $390892 | $148000 | +$242892 |
| 24 | $425345 | $154000 | +$271345 |
| 25 | $462290 | $160000 | +$302290 |
| 26 | $501905 | $166000 | +$335905 |
| 27 | $544384 | $172000 | +$372384 |
| 28 | $589934 | $178000 | +$411934 |
| 29 | $638777 | $184000 | +$454777 |
| 30 | $691150 | $190000 | +$501150 |
P = principal · PMT = contribution per compounding period · r = annual rate · n = periods per year · t = years. Assumes contributions align with the compounding period (this calculator compounds monthly, so n=12 makes PMT the monthly contribution). For monthly contributions at n≠12, convert to the monthly-equivalent rate first.
With monthly compounding at 7% on a starting 10,000 and 500/month contributed at the end of each period for 30 years:
The 2.5% inflation adjustment is based on the trailing 12-month CPI-U average. Actual inflation varies. Investment returns are not guaranteed. Past performance does not predict future results. This is for estimation only — consult a financial advisor.
The shaded band between the two curves is interest earned on interest. Compounding is slow at first, then accelerates — the longer the horizon, the wider the gap.
Compound interest is interest earned on both principal and accumulated interest. Enter your initial amount, monthly contribution, rate, and years to see your projected balance.
FreeToolHub Compound Interest Calculator is a free browser-based tool that projects investment growth with compound interest, no signup, no upload.
Calculate compound interest with optional monthly contributions. See year-by-year growth, real value after inflation. Free, no signup.
The Compound Interest Calculator projects how a starting balance plus regular deposits grows when interest earns interest — and can model the withdrawal (drawdown) phase too. Enter an initial principal, a monthly contribution, an annual rate, a horizon in years, and a compounding frequency from annually, semi-annually, quarterly, monthly, or daily; a timing toggle decides whether each deposit lands at the start or end of the period. Optional withdrawal modeling takes a fixed monthly amount starting in any year you choose and reports how long the balance lasts. Results report the final balance, effective APY, total contributions, total interest, the all-time return on money in, and the inflation-adjusted real value at 2.5%. An SVG growth chart plots balance against cumulative contributions, a switchable year-by-year or month-by-month schedule breaks down every period, and side-by-side scenario comparison plus a printable PDF report round out the output.
Long-term savers building retirement or college funds use it to test whether a target is reachable at a realistic rate. Young investors can see how starting a decade earlier beats contributing twice as much later, and renters weighing a brokerage account against a savings account can compare both. Financial-blog readers who encounter a 7% market average get a sandbox to pressure-test it with their own deposit schedule. Anyone deciding between monthly and daily compounding, or between contributing at the start versus the end of each month, can measure the actual dollar difference. Because results stay in your browser, it also suits shared computers when modeling family finances together.
(1) Enter your principal, monthly contribution, annual rate, years, frequency, and timing; the engine converts the rate into a per-period rate (annual rate divided by 1, 2, 4, 12, or 365). (2) It then simulates month by month: contributions are added at the chosen timing, and interest is credited only at the end of each compounding period, with daily compounding applied as 30 days of growth per month. Effective APY is derived as (1 + r/n)^n − 1, exposing what frequent compounding really adds. (3) The final balance is discounted by 2.5% inflation per year, based on the trailing 12-month BLS CPI-U average, so the real-value figure reflects genuine purchasing power.
The Rule of 72 is a mental shortcut for doubling time: divide 72 by your annual return percentage to estimate how many years an investment needs to double. At 6%, money doubles in roughly 12 years; at 9%, about 8. This calculator gives you the precise answer the rule approximates, and the difference matters at the extremes—daily compounding doubles noticeably faster than the estimate, while a 2% savings rate takes far longer than the rule's 36-year guess. It also highlights the inflation catch: after 2.5% annual erosion, your real doubling rate is closer to your nominal rate minus inflation, which the real-value line in the results makes visible.
Yes. Toggle "Model withdrawals (drawdown)" and enter a fixed monthly withdrawal plus the year it should begin — for example, contribute for 25 years, then draw $2,000 a month. The simulation continues month by month through the drawdown phase: interest still accrues, so if earnings outpace withdrawals the balance keeps growing, and the tool says so. If withdrawals exceed growth, the balance declines and the result reports exactly when it hits zero — for instance "balance lasts 18y 4m" — along with the total withdrawn. This makes it easy to test sustainable withdrawal rates: a classic check is whether 4% of the starting balance per year survives a 30-year retirement at your assumed return. The dynamic suggestion panel also flags unsustainable drawdowns with an explicit warning.
Over long horizons the projection is dominated by two inputs and one habit. The habit is contribution timing: start-of-month deposits compound one extra month each, which over 30 years adds roughly 2-3% to the final balance for free. The first dominant input is the return assumption — 6% versus 8% on a 30-year plan nearly doubles the outcome, which is why the comparison view exists: seeing a conservative and an optimistic path side by side beats trusting one number. The second is time itself, because compounding is back-loaded — in a 30-year projection the final five years often add more growth than the first fifteen. The monthly view of the schedule makes this visible: scroll to any year and the interest portion of that month's growth dwarfs the early years'. Withdrawals flip the same math against you, which is why the withdrawal schedule renders in a distinct view — the tool shows both the accumulation and the decumulation honestly rather than pretending the line only goes up.
For a diversified stock portfolio, historical US real returns sit near 7% nominal before inflation. A defensible planning band is 5-8%: run both ends through the comparison mode and plan against the lower path. Anything above 10% is speculative, and savings-account rates (3-5%) apply only to short horizons.
Each deposit compounds one extra month when made at the start, and over decades that compounds to roughly 2-3% more final balance — real money, though small next to the return assumption. Most retirement plans deposit per paycheck, which is effectively start-of-month.
Compound interest uses the formula A = P(1 + r/n)^(nt), where P is principal, r is annual rate, n is compounds per year, and t is years. This tool also supports monthly contributions (added at period end). It calculates year-by-year breakdown showing principal, interest earned, and total balance for each year.
Significant. $10,000 at 7% for 30 years without contributions grows to $76,123. Adding $500/month brings the total to $679,694—nearly 9x more. The tool shows this visually with a year-by-year table and inflation-adjusted values so you can see real purchasing power, not just nominal dollars.
This tool is also known by these tasks — each link opens the same tool with a focused guide:
Why did the fish get bad grades?
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