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Compound Interest Calculator

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Compound interest pays interest on interest, so a balance grows faster the longer it is left alone. Over twenty years the growth usually outweighs everything deposited, and over forty it dwarfs it.

Compound Interest Calculator - Danfio

https://danfio.com/tools/compound-interest-calculator/ - printed from this page

Currency: USD ($) - display only, nothing was converted

$

The balance you are starting with, from the account statement.

The nominal rate quoted on the account, before compounding is applied.

How long the money stays invested before you look at the result.

How often the account adds interest to the balance - it is in the account terms.

$

What you add each period, from your transfer schedule.

How often that deposit arrives.

Whether the deposit lands at the start or the end of each period; it moves the result slightly.

Used to restate the result in today money.

Leave at zero for a retirement account. A taxable account drags on the result each year.

$

Used to work out the deposit needed each period to get there.

Results update as you type. Nothing leaves your device.

Currency symbol

Symbol only - nothing is converted and no exchange rate is used. Figures quoted in the explanation text stay as the sources publish them.

Balance after 20 years

$144,572.72

$10,000 to start plus $48,000 of deposits at 7%

Total deposited
$58,000
Growth
$86,573 59.9% of the balance
Effective annual rate
7.23% Compounded 12 times a year
In today money
$88,229 At 2.5% inflation

Where the final balance comes from

  • Money you put in$58,000.00
  • Growth$86,572.72

The switch from one slice to the other is the point of compounding: late in the term the growth outweighs everything being paid in.

Year by year

YearStartDepositsGrowthEnd
1$10,000.00$2,400.00$801.42$13,201.42
2$13,201.42$2,400.00$1,032.85$16,634.27
3$16,634.27$2,400.00$1,281.01$20,315.28
4$20,315.28$2,400.00$1,547.11$24,262.39
5$24,262.39$2,400.00$1,832.45$28,494.83
6$28,494.83$2,400.00$2,138.41$33,033.24
7$33,033.24$2,400.00$2,466.49$37,899.74
8$37,899.74$2,400.00$2,818.29$43,118.03
9$43,118.03$2,400.00$3,195.52$48,713.55
10$48,713.55$2,400.00$3,600.02$54,713.58
11$54,713.58$2,400.00$4,033.77$61,147.34
12$61,147.34$2,400.00$4,498.86$68,046.20
13$68,046.20$2,400.00$4,997.58$75,443.79
14$75,443.79$2,400.00$5,532.35$83,376.14
15$83,376.14$2,400.00$6,105.79$91,881.93
16$91,881.93$2,400.00$6,720.67$101,002.60
17$101,002.60$2,400.00$7,380.00$110,782.60
18$110,782.60$2,400.00$8,087.00$121,269.60
19$121,269.60$2,400.00$8,845.11$132,514.70
20$132,514.70$2,400.00$9,658.02$144,572.72
Total$10,000.00$48,000.00$86,572.72$144,572.72

Deposits are spread evenly across the compounding periods, so a monthly deposit into a monthly-compounded account earns a full month of interest while the last one earns almost none.

What the rate does to the same plan

Annual rateEffective rateBalance after 20 yearsGrowth
3%3.04%$83,867.95$25,867.95
5%5.12%$109,333.14$51,333.14
7%7.23%$144,572.72$86,572.72
9%9.38%$193,668.89$135,668.89
10%10.47%$225,154.50$167,154.50

A single percentage point of return compounds into real money over a long horizon, and the gap between the highest and lowest rows here is the cost of paying an extra 1% in fees every year.

Hitting the goal

MeasureAmount
Goal$500,000.00
Already covered by the starting amount$10,000.00
Deposit needed monthly$882.30
Deposit needed per year$10,587.60
What the current deposit produces$144,572.72
Shortfall with the current deposit$355,427.28

Reaching $500,000 needs about $882.30 monthly at this rate, assuming the deposits keep their timing and the rate holds.

7% compounded 12 times a year pays an effective 7.23% a year, and a lump sum doubles in about 10.2 years. That is roughly 2 doublings over this horizon, which is why the growth slice grows so fast at the end of the term. In today money the final balance is worth $88,229, so inflation matters as much as the rate over decades.

This calculator compounds period by period, adds regular deposits at the start or end of each period, shows the effective annual rate behind the headline rate, and works out the deposit needed to reach a target.

About this compound interest calculator

Although the rate gets all the attention, the horizon is what turns a modest contribution into a large balance, because the last years compound on a base the early years never had. A single deposit doubles in roughly ten years at seven percent, and doubling again needs only the same wait.

The calculation works period by period rather than with a closed form, so deposits at the start or end of a period and a mid-term tax drag are both handled exactly, and the effective annual rate is shown behind the nominal one. Drawdown, contributions and inflation stay client-side in your browser, so nothing you enter is uploaded.

The growth is an estimate from the numbers you enter, not a forecast of a market. It assumes a constant rate, ignores the sequence of real returns, and leaves out expense ratios and capital gains tax on withdrawals. Feed it your own figures and compare a longer horizon against a higher contribution before you settle on a plan.

How this compound interest calculator works

The formula, and why the frequency matters

A lump sum compounds as balance × (1 + rate/periods)^periods. At a 7% nominal rate compounded monthly, the effective rate is 7.229% a year; compounded daily it is slightly higher still, and compounded annually it is exactly 7%. The headline rate is therefore never quite what you earn unless compounding happens once a year, which is why this page prints the effective annual rate separately.

Deposits compound as an annuity: each one earns interest for the number of periods it is invested. A deposit at the start of a period earns one period more than the same deposit at the end, which is the difference between an annuity due and an ordinary annuity - and the reason the deposit timing toggle exists. The calculation works period by period rather than with a closed form, so that timing lands exactly.

Time does more than the rate

A lump sum doubles in about 10 years at 7% (9.9 with monthly compounding), which is what the rule of 72 approximates: 72 divided by the rate gives 10.3 years. Extending a plan from 20 years to 30 does not add half again to the balance, it roughly doubles it, because the last years are compounding on a much larger base, and the growth slice - not the deposits slice - is what ends up dominating the chart.

The mirror image is that inflation works on the same principle in the other direction. At 2.5% a year, prices rise by more than a fifth over a decade, so a balance that looks large in 2060 money may be modest in today money. The page shows both the nominal balance and the figure restated in today money, so the nominal number does not flatter the plan.

Taxes, fees and the taxable account

In a taxable account, tax on dividends and realized gains takes money out of the compounding base every year, and the cost is larger than the same tax paid at the end, because the tax itself stops compounding. A retirement account defers it, so the whole balance keeps compounding - which is why the tax rate field belongs at zero for a 401(k) or IRA and above zero for a taxable brokerage account.

Fees are not a field here; they reach the result through the rate you enter. A 1% annual fee on a 7% return is not 1% of the outcome: it is about a quarter of the final balance over thirty years, because the fee compounds against you exactly as the return compounds for you. The rate table shows the gap between the 6% and 7% rows as the cost of that fee.

Where compounding works against you

The same arithmetic applies to debt, which is why a credit card at 24% doubles what you owe in about three years if nothing is paid. Savings and debt are the same formula with the sign reversed, which is why understanding compounding matters as much for the liability side as for the asset side.

That is the argument for contributing early rather than more: money invested at 25 has forty compounding years ahead of it, and money invested at 45 has twenty. The early money does less work but keeps working for longer, and time is the one variable in the formula that cannot be bought back later.

Worked examples

Each example below was run through the calculator on this page when the site was built, so the numbers match what you see when you enter the same inputs.

$10,000 plus $200 a month at 7% for 20 years

Starting amount: $10,000.00 · Annual interest rate: 7% · Years to grow: 20 · Compounding: Monthly · Regular deposit: $200.00 · Deposit frequency: Monthly · Inflation rate: 2.5% · Savings goal: $500,000.00

Balance after 20 years

$144,572.72

$10,000 to start plus $48,000 of deposits at 7%

Total deposited: $58,000 · Growth: $86,573 · Effective annual rate: 7.23% · In today money: $88,229

The deposits add up to $58,000 and the growth adds more than that on top, which is the whole argument for starting early.

The same plan over 30 years

Starting amount: $10,000.00 · Annual interest rate: 7% · Years to grow: 30 · Compounding: Monthly · Regular deposit: $200.00 · Deposit frequency: Monthly · Inflation rate: 2.5% · Savings goal: $500,000.00

Balance after 30 years

$325,159.17

$10,000 to start plus $72,000 of deposits at 7%

Total deposited: $82,000 · Growth: $243,159 · Effective annual rate: 7.23% · In today money: $155,017

Ten more years of the same $200 deposit more than doubles the balance, because the last decade compounds on a much larger base.

A $25,000 lump sum at 8% with no deposits

Starting amount: $25,000.00 · Annual interest rate: 8% · Years to grow: 25 · Compounding: Monthly · Regular deposit: $0.00 · Deposit frequency: Monthly · Inflation rate: 2.5% · Savings goal: $500,000.00

Balance after 25 years

$183,504.40

$25,000 to start plus $0 of deposits at 8%

Total deposited: $25,000 · Growth: $158,504 · Effective annual rate: 8.3% · In today money: $98,981

Nothing is added after the first deposit, yet the growth is several times the original amount: that is compounding working on a single sum.

Starting from nothing: $100 a month for 25 years

Starting amount: $0.00 · Annual interest rate: 6% · Years to grow: 25 · Compounding: Monthly · Regular deposit: $100.00 · Deposit frequency: Monthly · Inflation rate: 3% · Savings goal: $250,000.00

Balance after 25 years

$69,299.40

$0 to start plus $30,000 of deposits at 6%

Total deposited: $30,000 · Growth: $39,299 · Effective annual rate: 6.17% · In today money: $33,098

From zero, $100 a month at 6% becomes $69,299 in 25 years: $39,299 of growth on $30,000 deposited, or $33,098 in today money after 3% inflation. The deposit needed for a larger goal is what the Hitting the goal table shows.

Frequently asked questions

Does compounding monthly beat compounding annually?

Yes, but by less than people expect. A 7% nominal rate compounded monthly pays an effective 7.229% a year, roughly 0.23 percentage points more than annual compounding on the same money.

What return should I assume?

Use a range rather than a single number: the long-run return of a broad stock market index has been around 7% to 10% a year before inflation and fees in the historical US market record, using the long-run averages commonly cited in retirement research, such as the inflation-adjusted series behind the Trinity study. That is history, not a forecast: the sequence of returns matters and any single decade can be far away from the average. Run the calculator at 3% and 8% and plan for the middle.

Is compound interest taxable?

Interest and dividends are normally taxable in the year received in a regular account, while unrealized gains are not. Retirement accounts defer the tax, which is why the tax rate field belongs at zero for a 401(k) or IRA and above zero for a taxable brokerage account.

How much do fees cost over time?

A 1% annual fee on a portfolio returning 7% removes about a quarter of the final balance over thirty years, because the fee compounds against you exactly as the return compounds for you. Compare the rate table: the difference between 6% and 7% here is what that fee costs.

What is the rule of 72?

It is a mental shortcut for doubling time: divide 72 by the annual rate. At 8% that gives 9 years, against an exact 9.01 years. It is useful for checking whether a claimed return is plausible.

Should I add more each month or invest a lump sum early?

Time in the market does the work, so an earlier lump sum usually beats the same money dribbled in, at the cost of taking the risk immediately. Adding more each month is the practical answer for most people, because the deposit amount is the part you control.

Does inflation change the answer?

It changes what the answer means. At 2.5% a year, prices roughly double in 28 years, so a balance of $500,000 in 2054 buys about what $250,000 buys today. The calculator shows both figures so the nominal number does not flatter the plan.

Assumptions and sources

  • Standard future value, annuity and effective annual rate arithmetic, compounded each period, so start-of-period deposits and a mid-term tax drag are reflected.
  • This is not investment advice. Any rate entered here is an assumption, not a forecast, and real returns vary from year to year: a sequence of poor years early in a plan leaves less than the average rate suggests.
  • Inflation is a flat illustration rate; fees, withdrawal tax, contribution limits, RMDs and state tax are left out. Runs in your browser, nothing uploaded.

Last reviewed 2026-09-14. Not investment or insurance advice; quotes come from a licensed provider. Read the full disclaimer.

Where a figure on this page comes from an official agency — HUD, IRS, FICO or a state body — the site keeps a dated snapshot of the source page in its sources library, and a scheduled job re-checks that snapshot, so the number can be traced back to the document it came from.

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