Free tool
Compound interest calculator
See exactly how your money grows over time. Visual chart plus year-by-year breakdown. No signup.
Your inputs
Future value
$343,778
after 20 years
Growth: 164% from start
Total contributed
$130,000
your money
That's $500 per month for 20 years
Total interest
$213,778
earned over time
62% of your final balance
Growth over time
Year-by-year breakdown (20 rows)
| Year | Start | Contributed | Interest | End |
|---|---|---|---|---|
| 1 | $10,000 | $6,000 | $1,055 | $17,055 |
| 2 | $17,055 | $6,000 | $1,641 | $24,695 |
| 3 | $24,695 | $6,000 | $2,275 | $32,970 |
| 4 | $32,970 | $6,000 | $2,961 | $41,932 |
| 5 | $41,932 | $6,000 | $3,705 | $51,637 |
| 6 | $51,637 | $6,000 | $4,511 | $62,148 |
| 7 | $62,148 | $6,000 | $5,383 | $73,531 |
| 8 | $73,531 | $6,000 | $6,328 | $85,859 |
| 9 | $85,859 | $6,000 | $7,351 | $99,210 |
| 10 | $99,210 | $6,000 | $8,459 | $113,669 |
| 11 | $113,669 | $6,000 | $9,659 | $129,329 |
| 12 | $129,329 | $6,000 | $10,959 | $146,288 |
| 13 | $146,288 | $6,000 | $12,367 | $164,655 |
| 14 | $164,655 | $6,000 | $13,891 | $184,546 |
| 15 | $184,546 | $6,000 | $15,542 | $206,088 |
| 16 | $206,088 | $6,000 | $17,330 | $229,419 |
| 17 | $229,419 | $6,000 | $19,267 | $254,685 |
| 18 | $254,685 | $6,000 | $21,364 | $282,049 |
| 19 | $282,049 | $6,000 | $23,635 | $311,684 |
| 20 | $311,684 | $6,000 | $26,095 | $343,778 |
Want your investments tracked live with compound projections built in?
Open free in VekfinanceMost of the compounding magic happens in the last decade. Years 1-10 the line crawls. Years 20-30 it goes near-vertical. Starting early matters more than contributing a lot.
$200/month from 25 to 35 beats $200/month from 35 to 65
Both put in $200/month and earn 7% a year. The early saver contributes for just 10 years (ages 25 to 35), then never adds another dollar. The late saver contributes for 30 straight years (ages 35 to 65).
- Early saver: $200/mo ages 25 to 35, then leave it
- $281K
- Late saver: $200/mo ages 35 to 65
- $244K
- Total contributed (early saver)
- $24K
- Total contributed (late saver)
- $72K
→ The early saver puts in $48K less and still ends up about $37K ahead. A ten-year head start beats twenty extra years of contributing.
Where to put the money
- 1
401k up to the employer match
Free money. Most employers match 3-6% of your salary; you skip this only by leaving money on the table. Even if the fund options are bad, take the match.
- 2
Roth IRA up to the annual limit
$7,000 in 2025 ($8,000 if 50+). Tax-free growth forever. Best account in the US tax code for most middle-income people. Vanguard, Fidelity, or Schwab to open one in 10 minutes.
- 3
Back to 401k up to the annual limit
Once you've maxed Roth IRA, return to 401k contributions up to the $23,500 limit (2025). Tax-deferred growth, lowers your taxable income today.
- 4
Taxable brokerage for anything beyond
Same brokers. Low-cost index funds (VTI, VOO, VXUS). Tax efficient if you buy-and-hold rather than trade.
The 4% rule, quick
Target portfolio
25x
Your annual expenses
Safe withdrawal
4%
Per year, inflation-adjusted
Origin
Trinity study
Based on US market history
What the chart shows
One calculator vs the dashboard
This calculator models a hypothetical contribution schedule. Real life is messier (markets fluctuate, you pause contributions). The Vekfinance dashboard reads your real accounts, projects forward based on your current pace, and shows you how on-track you are toward retirement, a house down payment, or any custom goal. Free.
Frequently asked questions
What is compound interest?
Interest earned on both your original deposit AND the interest you've already earned. The longer the money sits, the more the interest itself earns interest, and balances grow faster than they would with simple interest.
How often does compounding actually happen?
Depends on the account. Savings accounts and CDs usually compound daily or monthly. Bond interest compounds at coupon dates (often semi-annual). Stock returns aren't really 'compounded' in the same way; gains accumulate continuously as the price moves. For most planning, monthly compounding is close enough.
What return rate should I use?
Current high-yield savings: about 4-5%. Long-run US stock market average (S&P 500): about 10% nominal, 7% real after inflation. Bonds: about 4-5%. A 60/40 stock/bond portfolio: about 7-8% historical. Use whatever you'd realistically expect for the kind of account you're modeling.
Is this calculator real-life accurate?
The math is exact. Real returns aren't exact: markets fluctuate year-to-year, you'll pause contributions sometimes, and inflation eats some of the gains. Use the calculator for direction-of-travel, not as a guarantee.
Does this account for taxes or inflation?
Neither. To see your inflation-adjusted return, subtract about 3% from the rate you enter (e.g., enter 7% to model a 10% nominal return after inflation). For taxes, if the money is in a 401k/IRA/HSA/Roth your gains are tax-advantaged so use the nominal rate directly. In a regular taxable account your real return is lower by your dividend / capital-gains tax rate.
Why does the chart show two lines?
The solid line is your total balance growing over time. The dashed line is just the money you contributed. The gap between them is interest you earned. Early in the timeline the lines are close together; over 20-30 years they diverge dramatically as compounding takes over.
Need a different calculator? Try our savings goal calculator, debt payoff calculator, or credit card payoff calculator.
Track your real portfolio
Vekfinance has built-in compound projections that pull from your real account balances. Free.
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