Compound interest calculator with deposits

Simulate compound interest with monthly contributions and an annual breakdown.

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Set your data

Initial capital (€)

Monthly contribution (€)

Effective annual return (%)

Duration (years)

Contributions at beginning of month

Set starting capital, monthly contribution, years and a hypothetical effective annual return. Choose end- or beginning-of-month contributions.

Result

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How to use the tool

Fill in these fields: Initial capital (€), Monthly contribution (€), Effective annual return (%), Duration (years), Contributions at beginning of month.
Select “Calculate” to obtain the result.
Set starting capital, monthly contribution, years and a hypothetical effective annual return.
Choose end- or beginning-of-month contributions.

Method and principles

Formula

r = {(1 + \frac{R}{100})}^{\frac{1}{12}} - 1

Contribution at month end

B_{m+1} = B_{m} \times (1 + r) + C

Contribution at month start

B_{m+1} = (B_{m} + C) \times (1 + r)

Method, examples and limits

The monthly rate is (1 + r)^(1/12) − 1, where r is the annual decimal rate. Each month growth is applied before the contribution, or after it for beginning-of-month deposits. €1000 at 5% annually with no contributions becomes €1050 after one year. The table separates contributions and returns. Taxes, fees and inflation are excluded; constant returns are an assumption, not a forecast or guarantee. Duration: 1–100 years.

Practical example

Input

Initial capital (€): 1000
Monthly contribution (€): 100
Effective annual return (%): 5
Duration (years): 10
Contributions at beginning of month: No

Result

€17,065.21

Result details

Result details
Parameter	Value
Contributed capital	€13,000.00
Simulated return	€4,065.21

Limits and checks

Limits and checks
Parameter	Value
Initial capital (€)	≥ 0; ≤ 1000000000
Monthly contribution (€)	≥ 0; ≤ 1000000000
Effective annual return (%)	≥ -99.99; ≤ 100
Duration (years)	≥ 1; ≤ 100

Reference sources

Investor.gov · Compound Interest Calculator

Frequently asked questions

Is the savings-plan return guaranteed?

No. This is a simulation using a hypothetical constant rate, excluding taxes, fees and inflation.

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