My Compound Interest - Personal Finance Projection
Personal finance projection

Compound Interest Calculator

Use this compound interest calculator with monthly contributions to estimate investment growth from an initial amount, monthly contribution, annual return and year by year projection.

Free tool No signup Browser-based calculations Not financial advice
Starting balance
Recurring monthly deposit
Investment horizon
20 years
Expected annual return
5.0%
Compounding frequency How often interest is applied
Used for inputs and results

Year-by-year projection

Annual snapshot of contributions, estimated interest and balance.

Year Total contribution Interest earned Projected balance
Adjust the calculator to see your projection.

How to read this projection

Start with the projected balance, then separate contributions from interest to see how much growth comes from compounding.

Inputs

Initial amount, monthly deposits, return, years and compounding frequency set the estimate.

Interpretation

Time and recurring deposits usually matter as much as the return assumption.

Limits

Taxes, fees, market volatility and changing returns are not included.

How the compound interest calculator works

The calculator keeps the assumptions visible so the projection stays easy to interpret.

Calculation methodology

The core formula is A = P x (1 + r/n)^(n x t), where the annual return is the estimate you enter, the compounding frequency sets how often interest is applied, and the time horizon sets the number of years.

Monthly contributions are modeled month by month and added at the end of each month, so each deposit starts compounding from the following month. Yearly compounding applies interest once per year, monthly applies it 12 times per year, and daily applies it more frequently, which can slightly increase the projected balance.

Results are estimates for planning only and are not financial advice. Taxes, fees, changing market returns and market volatility are not included.

Compound interest with monthly contributions

This calculator estimates growth from an initial amount and recurring monthly deposits. Monthly contributions can become a major part of the final balance because each deposit adds more money that can compound over time.

The time horizon and return rate strongly affect the result. The year by year table helps separate total contributions from interest earned, so you can see how much comes from deposits and how much comes from compound growth.

The Formula

The standard compound interest formula is:

A = P × (1 + r/n) ^ (n × t)

Where:

  • A = final amount
  • P = principal (initial investment)
  • r = annual interest rate (as a decimal)
  • n = number of times interest compounds per year
  • t = number of years

Compound interest example

Imagine you start with an initial amount of €5,000, add a monthly contribution of €250, use an expected annual return of 5%, and choose a 20 year time horizon. The calculator estimates the final balance, total contributions and interest earned based on these inputs.

Changing the monthly contribution, return rate or compounding frequency updates the projection immediately, so you can compare different investment growth assumptions without changing the structure of the plan.

Why start early?

The earlier you start, the more time compound growth has to work. Even if the monthly contribution stays the same, a longer time horizon gives each deposit more time to earn estimated returns.

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Understand your compound interest

Whether you're planning for retirement, building an emergency fund, or growing a long-term investment, understanding how compound interest works is the foundation of every smart financial decision.

Compound interest means your balance grows from both the money you invest and the returns already earned in previous periods. Unlike simple interest, the interest itself earns interest over time.

The standard formula is A = P x (1 + r/n)^(n x t). This calculator also models monthly contributions by adding each deposit at the end of the month and compounding it from the following month.

Monthly contributions steadily increase the base amount that can compound. Over long time horizons, recurring deposits can become a major part of the final balance and can also earn interest themselves.

Use the frequency that matches the account or investment assumption you are modeling. Daily compounding is slightly higher than monthly, and monthly is slightly higher than yearly, because interest is added more often.

Yes. You can use it to estimate investment growth by entering an initial amount, monthly contribution, annual return, compounding frequency and time horizon. Results are estimates, not guaranteed returns.

Yes. The projected balance is the future value of the initial amount, monthly contributions and estimated compound growth over the selected time horizon.

With simple interest, you earn returns only on the original principal. With compound interest, you earn returns on both the principal and accumulated interest, so the gap can become large over long periods.

No. This calculator is an educational planning tool. It does not account for taxes, fees, market volatility or your personal financial situation.