Compound interest calculator with inflation and fees

Name: Compound interest calculator
Author: Richard Injante

How much your money grows with regular contributions, and what it is really worth once inflation and fees are taken off.

Content reviewed by Richard Injante Published by SolucionesAhora.com Updated on 2026-10-08 How we verify

Calculator inputs

Enter your figures, or press “See example” to watch it work.
If your case is unusual, open “Advanced options”.
Read the result and, below it, what it means and how it was worked out.

Initial capital

The money you start with. It can be zero if you will only make regular contributions.

Annual interest or return %

The expected annual nominal return, before fees and inflation. For a savings account, the nominal rate; for an investment, a cautious long-term estimate, not the best year’s figure.

Years

How long you let the money grow. Compound interest gives its biggest results over long periods: half of the growth comes in the last few years.

Compounding

How often interest is added to the capital. The more often, the slightly higher the effective return; the difference between monthly and daily is small.

Contribution each period (optional)

What you add at the end of each compounding period (with monthly compounding, what you save per month). It is what weighs most in the long-run result.

Optional

Advanced options

Expected annual inflation (optional) %

The yearly rise in prices you expect. It shows what the result will be worth in today’s money: the same capital buys less as years pass. As a long-run reference, many central banks target about 2%.

Optional

Annual product fee (optional) %

What the fund or manager charges each year, as a % of capital. It is subtracted from the return. A 1% yearly difference looks small, but over 30 years it eats between 18% and 25% of the result, depending on whether you keep contributing.

Ongoing charges (TER) or management fee

See the result

Results

Final balance125,510.22

Interest earned67,510.22

Total you contributed58,000

Money multiplier2.164

Value in today’s money125,510.22

Real annual return6 %

Effective annual return6.168 %

Years to double the money11.6

Year by year growth
Year	Contributed	Accumulated interest	Balance	Balance in today’s money
1	12,400	683.89	13,083.89	13,083.89
2	14,800	1,557.99	16,357.99	16,357.99
3	17,200	2,634.03	19,834.03	19,834.03
4	19,600	3,924.46	23,524.46	23,524.46
5	22,000	5,442.51	27,442.51	27,442.51
6	24,400	7,202.21	31,602.21	31,602.21
7	26,800	9,218.48	36,018.48	36,018.48
8	29,200	11,507.14	40,707.14	40,707.14
9	31,600	14,084.97	45,684.97	45,684.97
10	34,000	16,969.84	50,969.84	50,969.84
11	36,400	20,180.66	56,580.66	56,580.66
12	38,800	23,737.54	62,537.54	62,537.54
13	41,200	27,661.83	68,861.83	68,861.83
14	43,600	31,976.19	75,576.19	75,576.19
15	46,000	36,704.68	82,704.68	82,704.68
16	48,400	41,872.83	90,272.83	90,272.83
17	50,800	47,507.78	98,307.78	98,307.78
18	53,200	53,638.3	106,838.3	106,838.3
19	55,600	60,294.96	115,894.96	115,894.96
20	58,000	67,510.22	125,510.22	125,510.22

See the working step by step

Effective annual return = 6.168 %
Real annual return = 6 %

Free, no sign-up! What if you could do this without a calculator? A five-minute game with challenges, lives and points. It clicks even when you cannot be bothered.

In short

What it calculates: How much your money grows with regular contributions, and what it is really worth once inflation and fees are taken off.
Formula used: Net return = return − annual fee
Example: Example 1. Capital and contributions over 20 years.

Compound interest calculator

Compound interest is what happens when interest earns interest too: money grows faster and faster. But there are two things almost every calculator ignores that change the result a lot: inflation, which reduces what money buys, and fees, which take a slice of the return every year.

Enter the capital, the return, the years and the regular contribution; under advanced options, add the expected inflation and the annual fee. You get the final balance, what it is worth in today’s money, the real return and a chart of what you paid in, the balance and its real value. Everything runs in your browser.

How it works

In each compounding period the period’s interest is added to the balance and then the contribution is added. With monthly compounding, every month the balance is multiplied by (1 + annual rate / 12) and then what you contribute is added.

The annual fee is subtracted from the return before calculating. Inflation is discounted at the end: each year’s balance is divided by (1 + inflation) raised to that number of years, which gives its value in today’s money. The real return is the annual growth in purchasing power: (1 + net return) ÷ (1 + inflation) − 1.

Formula

Net return = return − annual fee
Final balance = P · (1 + i)^n + A · ((1 + i)^n − 1) / i with i = net return / periods per year and n = total periods
Value in today’s money = final balance ÷ (1 + inflation)^years
Real return = (1 + net return) ÷ (1 + inflation) − 1
Effective annual return = (1 + i)^periods − 1
Years to double = ln 2 ÷ ln(1 + effective return) (rule of 72: 72 ÷ return in %)

Worked example

Example 1. Capital and contributions over 20 years.
Starting with $10,000 and adding $200 a month for 20 years at 6% with monthly compounding, the final balance is $125,510. You paid in $58,000 and interest generates $67,510: your money multiplies by 2.16. At this return it doubles every 11.6 years.

Example 2. Taking off inflation.
The same case with 2.5% annual inflation: the $125,510 at the end will be worth $76,595 in today’s money. The real return is not 6% but 3.41% a year. That is the figure to plan with.

Example 3. The effect of a fee.
If the fund also charges 0.6% a year, the final balance falls to $115,489 ($10,021 less) and, in today’s money, to $70,480. The real return drops to 2.83%. A fee that looks small eats almost 8% of the result over 20 years.

Example 4. No contributions.
$5,000 at 4% compounded yearly for 15 years: $9,004.72. It almost doubles without doing anything; that is the effect of time.

Explanation

What compound interest is

With simple interest only the initial capital earns interest. With compound interest, interest is added to the capital and starts earning interest itself. The result is exponential growth: slow at first and ever faster. That is why time and consistency matter more than the exact return.

Why inflation matters

$100,000 in 30 years does not buy what it does today. If prices rise 2.5% a year, that $100,000 will be worth around $48,000 in today’s money. Planning with nominal figures gives a false sense of security: what counts is the real return, which is calculated by taking off inflation.

Why fees matter

Fees are charged every year on all the capital, not just the gains, and they also compound. A 1% yearly difference between two funds with the same gross return can mean between 18% and 25% of the final balance after 30 years.

The rule of 72

Dividing 72 by the annual return (in %) estimates how many years the money takes to double: at 6%, about 12 years; at 3%, about 24. It is an approximation; the calculator gives the exact figure.

Common mistakes

Using the best period’s return as if it were the expected one.
Ignoring inflation and fees.
Starting late: a year’s delay at the start costs far more than one at the end.
Stopping contributions during market falls.
Confusing the nominal rate with the effective one.

Limits of this calculator

It assumes a constant return every year. A real investment fluctuates, and the result also depends on the order of good and bad years.
Contributions are made at the end of each period and stay the same; they do not rise with inflation.
It does not include tax on gains.
Fees are subtracted from the annual return; it does not model entry or exit charges.
It accepts up to 100 years.

Notice

The result is a projection with the assumptions you enter, not a promise of returns or financial advice.

Frequently asked questions

What is compound interest?

Interest calculated on the initial capital plus the interest already accumulated. It makes money grow exponentially instead of linearly.

How is compound interest with monthly contributions calculated?

In each period the interest is added to the balance and then the contribution. The closed formula is P·(1+i)^n + A·((1+i)^n − 1)/i, and the calculator applies it for you.

What is the real return?

The return after taking off inflation (and, here, fees): it measures how much your purchasing power grows, not just the figure in your account.

How much does a fund fee matter?

More than it seems: it is charged every year on all the capital. At 0.6% a year over 20 years, the example’s result falls 8%; at 1.5%, much more.

What is the rule of 72?

A shortcut to estimate how many years money takes to double: 72 divided by the annual return in %. At 6% it is about 12 years.

Which compounding frequency should I choose?

The one your account or product uses. The more frequent, the slightly higher the effective return, but the difference between monthly and daily is tiny.

Can I use it for a debt?

Yes: the same calculation shows how an unpaid debt grows. For fixed-payment loans, use the loan calculator.

Is my data sent to a server?

No. The calculation runs in your browser.

Sources and references

The formula behind this calculator is not ours. These are the sources it comes from, in APA 7 format, in case you want to go to the original or cite them in your own work.

Brealey, R. A., Myers, S. C., & Allen, F. (2020). Principles of corporate finance (13.ª ed.). McGraw-Hill Education. Future value with compound interest and regular contributions (annuities).
Fisher, I. (1930). The theory of interest. Macmillan. The relationship between nominal rate, inflation and real rate used to compute the real return.

Need to calculate something else?

These tools are often used alongside this calculator.