Current for 2026•As of: July 2026

Interest Calculator calculate compound interest.

Calculate interest & compound interest: final capital, return and wealth development.

FreeNo sign-upGDPR-compliant
€
0 €500,000 €

Terms

%
0.0 %15.0 %
years
1 years50 years

Interest is added to the capital

Savings plan (optional)

€
0 €2,000 €

Rule of 72

Divide 72 by the interest rate to get the approximate doubling time. At 5%, your capital doubles in approx. 14.4 years.

Final capital

16,288.95 €

after 10.0 years

Interest earned

+6,288.95 €

+62.9%

Total deposits

10,000.00 €

Capital + savings rate

Overview

Initial capital10,000.00 €
Interest rate (nominal)5.00 %
Term10.0 years
Final capital16,288.95 €

Compound interest curve

Zeitreihen-Diagramm: Capital endet bei 16,288.95 €.0.00 €4,072.24 €8,144.48 €12,216.71 €16,288.95 €1357910Years
  • Capital

Capital growth

YearCapitalDepositInterest
110,500.00 €-+500.00 €
211,025.00 €-+525.00 €
311,576.25 €-+551.25 €
412,155.06 €-+578.81 €
512,762.82 €-+607.75 €
...
1016,288.95 €-+775.66 €

Compound interest formula:

Kn = K0 × (1 + r)n

K0 = initial capital, r = interest rate, n = years

Important note

These calculations are for non-binding information only and do not replace professional tax advice. All information without guarantee. Learn more

Sources & calculation basis

Our calculations are based on the following official sources (as of: July 2026):

Related guides

Building Wealth

Interest calculator: everything about interest and compound interest

Our interest calculator helps you plan your investment. Calculate how your capital develops over time – with or without regular deposits.

What is compound interest?

Compound interest arises when earned interest is added to the capital and is itself compounded in the next period. This effect leads to exponential growth of your wealth.

Compound interest effect: €10,000 at 5% interest over 20 years

Compound interest effect: €10,000 at 5% interest over 20 years
ItemAmount
Simple interest: €10,000 + (€10,000 x 5% x 20)€20,000
Compound interest: €10,000 x (1.05)^20€26,533

The compound interest formula: K_n = K_0 x (1 + r)^n

The compound interest formula: K_n = K_0 x (1 + r)^n
ItemAmount
K_n = final capital-
K_0 = initial capital-
r = interest rate (as a decimal, e.g. 0.05 for 5%)-
n = number of years-

Key concepts

Rule of 72
A simple rule of thumb for calculating the doubling time: doubling time = 72 / interest rate. At 6% interest, your capital doubles in about 12 years (72 / 6 = 12).
Annual compounding
5.00% nominal = 5.00% effective
Monthly compounding
5.00% nominal = approx. 5.12% effective
Effective vs. nominal
With sub-annual compounding (e.g. monthly or quarterly), the effective annual interest rate is higher than the nominal interest rate.

Savings plan formula: FV = PMT x ((1 + r)^n - 1) / r

Savings plan formula: FV = PMT x ((1 + r)^n - 1) / r
ItemAmount
PMT = monthly savings rate-
r = monthly interest rate-
n = number of months-

Application examples

Retirement planning
How much do I need to save monthly to have €500,000 by age 67?
Savings/fixed deposit
What does my fixed deposit yield at 3.5% after 2 years?
ETF savings plan
How does a savings plan with €200 per month develop at 7% return?
Inflation offset
What return do I need to offset inflation?

Investment tips

  1. Time is money: The earlier you start, the stronger the compound interest effect.
  2. Save regularly: Even small amounts add up over the years.
  3. Consider inflation: The real return is the interest rate minus the inflation rate.
  4. Diversify: Spread your capital across different asset classes.

Note

These calculations are for illustration purposes only and do not replace professional financial advice. Past returns are no guarantee of future returns. Also note taxes on capital gains (capital gains tax: 25% plus solidarity surcharge plus church tax if applicable).

Frequently Asked Questions

Compound interest arises when earned interest is added to the capital and is itself compounded in the next period. This effect leads to exponential growth of your wealth. Example: with €10,000 initial capital and 5% interest over 20 years, simple interest results in €20,000, while compound interest results in €26,533.

The mathematical formula for compound interest is: K_n = K_0 × (1 + r)^n. Here, K_n is the final capital, K_0 is the initial capital, r is the interest rate (as a decimal, e.g. 0.05 for 5%), and n is the number of years.

The rule of 72 is a simple rule of thumb for calculating the doubling time: doubling time ≈ 72 ÷ interest rate. At 6% interest, your capital doubles in about 12 years (72 ÷ 6 = 12). This rule works best for interest rates between 4% and 12%.

With sub-annual compounding (e.g. monthly or quarterly), the effective annual interest rate is higher than the nominal interest rate. Example: with annual compounding, 5.00% nominal equals 5.00% effective. With monthly compounding, however, 5.00% nominal results in approximately 5.12% effective.

With a savings plan, you pay in a fixed amount at regular intervals. The formula for calculating the future value of an ordinary annuity is: FV = PMT × ((1 + r)^n - 1) / r. Here, PMT is the monthly savings rate, r is the monthly interest rate, and n is the number of months.

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