Compound Interest Calculator

See how a starting amount and regular deposits grow with compound interest — set your rate, term and how often it compounds to get the future balance and the interest earned.

Your plan
Results
Future balance
Total deposited
Interest earned
Year-by-year growth
YearDepositedInterestBalance
Enter your starting amount, deposit, rate and term to project the balance.

Every calculation runs in your browser — the amounts you enter never leave your device.

FAQ

How is the balance worked out?

Your starting amount grows by compound interest for the whole term, and each regular deposit is added and then compounds as well. The future balance is those two parts together; the interest earned is the balance minus everything you paid in.

What does the compounding frequency change?

It sets how often interest is added and how often your deposit goes in. Compounding monthly instead of yearly grows the balance a little faster at the same rate, and your deposit counts as that period’s amount — per month, per quarter, and so on.

When are the deposits counted?

Each deposit lands at the end of every compounding period, so the first one starts earning from the next period, while the starting amount earns from the outset. Set the deposit to zero to see growth from the starting amount alone.

Can I rely on this for real decisions?

Treat it as an estimate for learning and rough planning, not advice. It assumes one steady rate for the whole term and leaves out inflation, taxes, fees and market swings, so a real account will differ — check with a licensed professional before deciding.

Written and reviewed by the BroBroGo editorial team.Last updated:

How Compound Interest Works

Compound interest is the process where an investment earns interest on both the original starting amount and the accumulated interest from previous periods. Unlike simple interest, which only calculates returns on the initial principal, compounding allows an asset to grow at an accelerating rate over time.

This calculator projects how a starting balance and regular contributions grow under different compounding schedules. The calculation relies on several key inputs:

  • Starting amount: The initial sum of money placed into the investment at the beginning of the term.
  • Regular deposit: An additional sum added to the investment at the end of each compounding period.
  • Annual interest rate: The percentage rate of interest earned per year.
  • Years: The duration of the investment, which must be a whole number from 1 to 100.
  • Compounding: The frequency at which interest is calculated and added to the balance, with options including Yearly, Every 6 months, Quarterly, Monthly, and Daily.

The Impact of Compounding Frequency and Regular Deposits

The frequency of compounding determines how often interest is calculated and added to the principal balance. When interest compounds more frequently, such as monthly or daily rather than yearly, interest is earned on previously accumulated interest sooner. This higher frequency results in a larger future balance over time, even when the annual interest rate and total deposits remain identical.

Regular deposits accelerate wealth building by consistently increasing the principal base that earns interest. Under the rules of this calculator, each regular deposit is counted at the end of every compounding period. This means the starting amount earns interest from the very beginning of the timeline, whereas the first regular deposit begins earning interest from the second period onward. If you set the regular deposit to zero, the tool projects growth based solely on the starting amount.

Interpreting the Calculation Results

Once the inputs are processed, the tool generates three primary output metrics to help you evaluate the investment trajectory:

  • Future balance: The total projected value of the investment at the end of the specified term.
  • Total deposited: The sum of the starting amount and all regular deposits made over the years.
  • Interest earned: The total interest generated by the investment, calculated as the future balance minus the total deposited.

The tool also generates a Year-by-year growth table. This table breaks down the financial progression annually, allowing you to track the compounding effect over time through four distinct columns:

  1. Year: The specific year of the projection.
  2. Deposited: The cumulative amount of money you have contributed up to that year.
  3. Interest: The cumulative interest earned up to that year.
  4. Balance: The total value of the investment at the end of that year.

Calculation Rules and Error Handling

To ensure realistic and mathematically sound projections, the calculator operates under specific rules and validation constraints:

  • Negative Values: Amounts and rates cannot be negative. If a negative value is entered, the balance displays "—" and the error message "Amounts and rate can’t be negative." appears.
  • Zero Interest: If the annual interest rate is set to 0, the interest earned will be 0.00 and the future balance will equal the total deposited.
  • Term Limits: The investment term must be a whole number of years between 1 and 100. Entering an invalid term triggers the error message "Enter a whole number of years from 1 to 100.".
  • Value Limits: If the input numbers are too large to project, the tool displays the error message "Those numbers are too large to project.".
  • Invalid Inputs: For any other non-numerical or invalid entries, the tool displays "Enter valid numbers to calculate.".

Data Privacy and Processing

This calculator is designed with a strict local processing model. Every calculation runs directly in your browser, meaning the financial figures, interest rates, and terms you enter never leave your device and are not uploaded to any external servers.

Limitations of Financial Projections

While compound interest calculations are valuable for learning and planning, these results are estimates only and do not represent guaranteed financial returns. The calculator assumes a perfectly steady interest rate and uninterrupted regular deposits over the entire term. In real-world scenarios, investment performance fluctuates, and actual returns will differ due to factors not accounted for by this tool, including inflation, taxes, and account fees.

Frequently Asked Questions

How is the balance worked out?

Your starting amount grows by compound interest for the whole term, and each regular deposit is added and then compounds as well. The future balance is those two parts together; the interest earned is the balance minus everything you paid in.

What does the compounding frequency change?

It sets how often interest is added and how often your deposit goes in. Compounding monthly instead of yearly grows the balance a little faster at the same rate, and your deposit counts as that period’s amount — per month, per quarter, and so on.

When are the deposits counted?

Each deposit lands at the end of every compounding period, so the first one starts earning from the next period, while the starting amount earns from the outset. Set the deposit to zero to see growth from the starting amount alone.

Can I rely on this for real decisions?

Treat it as an estimate for learning and rough planning, not advice. It assumes one steady rate for the whole term and leaves out inflation, taxes, fees and market swings, so a real account will differ — check with a licensed professional before deciding.

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