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Calculators · Updated October 25, 2026 · Reviewed by FormatFlow Editorial

Compound Interest Calculator — Future Value

You can calculate the future value of a starting balance plus regular monthly contributions, see the interest earned and track the balance year by year at monthly, quarterly or annual compounding.

Runs in your browserFree · No sign-up · No watermark
Compound growthRuns in your browser
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Everything runs locally in this tab. No file is uploaded while the tool loads.

This tool runs in your tab. Nothing is uploaded and no copy is stored.

How files are handled

At a glance

Works with
Compound growth
Processing
In your browser
Price
Free, no account
Updated
October 25, 2026
All Calculators

About Compound Interest Calculator

Compound interest grows a balance by applying interest to both the original amount and the interest already earned. A single lump sum does this on its own, and regular monthly contributions add fuel: each deposit starts earning interest for the rest of the timeline. This calculator combines the two and shows the split between money you paid in and money the balance earned.

Compounding frequency changes the result because interest is added more or less often. Monthly compounding is the usual default, quarterly is common for some savings products, and annual compounding is the simplest to compare. The tool also asks whether contributions arrive at the start or the end of each month, because a deposit made at the start earns one extra month of interest, which adds up over decades.

What this tool does

The details that matter when you use Compound Interest Calculator for real work.

  • Lump sum plus monthly deposits

    Start with an initial balance and add a fixed contribution every month for the whole period.

  • Three compounding frequencies

    Choose monthly, quarterly or annual compounding and see how the frequency changes the future value.

  • Start or end of month

    Decide whether each deposit is added before or after that month's interest, which matters over long periods.

  • Year-by-year table

    A compact table shows cumulative contributions, cumulative interest and the closing balance for each year.

  • Clear contribution split

    The summary separates what you paid in from what the balance earned, so growth is not confused with savings.

  • Copy and reset

    Copy the future value into a plan or spreadsheet, or reset every input and start again.

How to use Compound Interest Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Enter the starting balance

    Type the lump sum you already have invested; leave the monthly contribution at zero if there is none.

  2. 02

    Add a monthly contribution

    Enter the amount added each month, or zero for a single deposit.

  3. 03

    Set the annual rate and years

    Use the nominal annual rate and the number of years to model; fractional years are converted to whole months.

  4. 04

    Choose the compounding

    Select monthly, quarterly or annual compounding and whether contributions arrive at the start or the end of the month.

  5. 05

    Review the year-by-year table

    The table separates cumulative contributions from cumulative interest and shows the balance at each year end.

How this tool works

Works with
Compound growth
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • The rate is held constant for the whole period; real investment returns vary.
  • Taxes, fees, inflation and increases to the contribution are not modelled.
  • Contributions stay at the amount entered and continue for every month of the term.
  • Results use a nominal annual rate and assume interest is credited each compounding period.

Privacy and file handling

Everything is computed in your browser from the numbers you type; no balance, contribution or rate is submitted to a server. Nothing is stored between visits and no account or email is required, so the what-if scenarios you try stay on your device.

Read the full privacy policy

Compound Interest Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
What is compound interest?
Compound interest means each period's interest is added to the balance and then earns interest itself in later periods. The longer the money stays invested, the more of the final balance comes from interest rather than from deposits.
How are monthly contributions handled?
Each contribution is added to the balance and compounds at the monthly equivalent of the annual rate. Choosing start-of-month timing makes every deposit earn one extra month of interest compared with end-of-month timing.
How do you convert the annual rate for monthly compounding?
The nominal annual rate is divided across compounding periods, then converted to a monthly equivalent with i = (1 + r/n)^(n/12) − 1. That keeps effective annual growth consistent with the frequency you choose.
Why does compounding more often produce a slightly larger balance?
Interest added more often starts earning interest sooner. The effect is small at low rates and short horizons but grows with the rate and the number of years, which is why the effective annual rate exceeds a simple annual rate.
Does the calculator include taxes, fees and inflation?
No. It models nominal growth before tax, fees and inflation. Real returns will be lower once those are accounted for, and tax rules vary by country and account type.
Can I model a zero interest rate?
Yes. At zero percent the balance is simply the starting amount plus all contributions, which is a useful way to check the table and compare against a savings account.
What happens with fractional years?
The number of periods is rounded to the nearest month, so 10.5 years becomes 126 monthly periods. The table labels each completed year and the final partial year.
Is this a prediction of investment returns?
No. It is a deterministic calculation for a rate you choose, not a forecast. Real markets fluctuate, and an investment that pays a fixed annual rate is unusual outside savings products.