Interest Calculator
Calculate interest & compound interest: final capital, return and wealth development.
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More detailscompound interest · Annually · no regular savings
Compounding
Only when calculating the final capital
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Reach the goal via
€10,000.00 grows to €16,288.95 after 10 years at 5% interest – €6,288.95 in interest.
- 10 yrFinal capital €16,289
- 10 yrFinal capital €16,289
- Initial capital
- €10,000.00
- Interest earned+62.9%
- + €6,288.95
- Final capital
- €16,288.95
- Interest rate (nominal)
- 5%
- Term
- 10 years
- Total deposits
- €10,000.00
What you can do
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.
At 6% interest+€1,620
Final capital then €17,908.
How this was calculated
Solving for the final capital. With interest paid more than once a year, the annual rate is split across the periods; regular savings also earn interest.
RZ-26 · headon.pro
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.
- Simple interest: €10,000 + (€10,000 x 5% x 20)
- €20,000
- Compound interest: €10,000 x (1.05)^20
- €26,533
- K_n
- final capital
- K_0
- initial capital
- r (5% = 0.05)
- interest rate as a decimal
- 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
- 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
- 1Time is moneyThe earlier you start, the stronger the compound interest effect.
- 2Save regularlyEven small amounts add up over the years.
- 3Consider inflationThe real return is the interest rate minus the inflation rate.
- 4DiversifySpread 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
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. 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.
What is the compound interest formula?
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.
What is the rule of 72?
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%.
What is the difference between the effective and nominal interest rate?
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.
How does the savings plan calculation work?
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.