Compound Interest Calculator for Traders and Investors

GradTraders

Compound Interest Calculator for Traders and Investors

Use this free compound interest calculator to test how a starting balance, monthly contributions, an expected annual return, investment period, annual fee and inflation could affect long-term growth. Compare cautious, expected and optimistic scenarios, or use Trader-to-Investor mode to model investing part of withdrawn trading profits. No account, email address or sign-up is required, so you can bookmark the calculator and reuse it whenever your assumptions change.

We have tried to build the best compound interest calculator on the internet: free, clear enough to use without financial jargon, and useful enough to bookmark and return to whenever your figures or circumstances change.

Free to use No sign-up No email required Instant results Bookmark and reuse

By Matthew Jackson · GradTraders · Updated 21 July 2026

Step 1Enter your balance, monthly amount, expected annual return and investment period.
Step 2Review projected growth, contributions, annual fee, annual inflation and three scenarios.
Step 3Change the assumptions, then bookmark the page or save a shareable scenario.

Compound Interest Calculator (free, no sign up)

Choose a mode, then enter the main figures you want to test. Results update automatically, or you can press Calculate growth. Open Advanced options to include fees, inflation, compounding frequency, contribution timing and a wider or narrower scenario range. Nothing is locked behind registration. The results, chart, milestones and year-by-year table all recalculate from the valid inputs currently shown.

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Your assumptions

How to enter the figures: percentage fields use ordinary numbers, so 5 means 5%. Enter the investment period as a whole number of years.

The amount already invested today.
What you plan to add each month.

Enter 5 for a 5% annual return assumption. This is a projection, not a guarantee.
Enter a whole number from 1 to 60. For example, 20 means 20 years.
Advanced options
Enter the yearly fee percentage. Use 0 if there is no annual fee, or 0.25 for a 0.25% annual fee.
Enter the assumed yearly inflation rate. For example, 2.5 means 2.5%.
For most general investment projections using an expected annual return, select Annually. Choose another frequency only when the account or product states that growth is credited and reinvested that often.
Beginning-of-month contributions receive one extra month of potential growth.
Enter the percentage-point range. At 7 with a range of 3, the calculator compares 4%, 7% and 10%.
Expected projected value £0

Enter your assumptions to calculate a projection.

Total contributed £0 Starting balance plus regular additions
Estimated growth £0 Projected value above contributions
Today’s-money value £0 Adjusted for inflation
Estimated fee drag £0 Difference versus the same return before fees
Growth share 0% Share of the final value created by growth
Monthly amount invested £0 Regular monthly contribution
Cautious £0 0% annual return
Expected £0 0% annual return
Optimistic £0 0% annual return
Results based on your current inputs The chart, milestones and annual table will recalculate whenever you change a valid input.

Projected growth based on your current inputs

All three lines recalculate from the inputs above. They are smooth mathematical projections; real investment returns normally rise and fall from year to year.

Estimated milestones based on the expected scenario

These dates recalculate from your current starting balance, monthly contribution, expected return, annual fee, investment period, contribution timing and compounding selection.

Year-by-year projection based on your current inputs

Compound growth projection by year based on the current calculator inputs
YearContributedCautiousExpectedOptimistic

How to Use This Compound Interest Calculator

This compound interest calculator is designed to answer a practical question: how could a lump sum and regular contributions change over time under different assumptions? Work through the fields in order rather than trying to guess a final balance.

Choose the right mode

Use Standard Investor for a starting balance and normal monthly contributions. Use Trader-to-Investor when part of withdrawn trading profits will be redirected into a separate long-term portfolio.

Enter the starting amount

Add the amount already invested. Enter zero when you are starting from nothing. Money fields accept plain figures such as 10000 and formatted figures such as 10,000 or £10,000.

Add a monthly contribution

Enter an amount you could contribute consistently. Testing several realistic monthly amounts often provides more useful planning information than changing the assumed return.

Set return and time

Choose an annual return assumption and an investment period from 1 to 60 whole years. Treat the return as an illustration, not a promise or prediction.

Review advanced options

Add an annual fee and annual inflation assumption, choose the compounding frequency that matches the account or product, and decide whether contributions arrive at the beginning or end of each month.

Compare, change and save

Read the three scenarios, chart and annual table. Change one assumption at a time, then copy a shareable link, download the CSV or bookmark the page for later.

Which Compounding Frequency Should You Choose?

Compounding frequency describes how often growth is credited to the balance and becomes part of the amount that can earn future growth. The most accurate selection is not automatically the option that produces the largest result. It is the option that most closely matches the account, investment product or interest calculation you are modelling.

Annually

Use this for most general long-term investment projections. When you are entering an estimated annual return for shares, ETFs, funds or a diversified portfolio, Annually is the clearest default and avoids making the projection look larger merely because a more frequent nominal compounding setting was chosen.

Quarterly

Choose Quarterly when the provider credits and reinvests interest, income or growth approximately every three months, or when the product documentation explicitly states quarterly compounding.

Monthly

Choose Monthly when an account or product explicitly credits and reinvests interest or growth every month. This may be relevant to some savings products and fixed-interest accounts.

Daily

Choose Daily only when the provider specifically states that interest is compounded daily. Daily compounding normally produces the largest projection when the same nominal annual rate is entered, but that does not make it the most realistic choice.

GradTraders guidance: for a normal investment projection using an expected annual return, select Annually. For a savings account, cash product or fixed-interest account, check the provider’s documentation and use its stated compounding frequency.

How the Compound Interest Calculator Can Help

This compound interest calculator cannot tell you what markets will return. It can help you understand which parts of a long-term plan are under your control and how sensitive the result is to uncertain assumptions.

Test contribution levels

Compare what happens when the monthly contribution changes while the return and time period remain the same.

Compare time horizons

See how extending or shortening the investment period changes the balance and the share produced by growth.

Stress-test return assumptions

Use the cautious, expected and optimistic scenarios to avoid relying on one precise percentage.

See fees and inflation

Compare the headline future value with estimated fee drag and an approximate value in today’s spending power.

Separate trading from investing

Model regular transfers from trading profits without pretending that the trading account itself compounds smoothly.

Build a repeatable planning habit

Bookmark the tool and rerun it when contributions, costs, goals or circumstances change.

How to Read the Calculator Results

The compound interest calculator’s largest number is the expected projected value after the annual fee assumption. It is supported by several results that explain where that balance came from and how much confidence to place in it.

Total contributed

Your starting balance plus every monthly addition. This is the amount supplied by you rather than created by projected growth.

Estimated growth

The expected projected value minus total contributions. It can be negative when the net return assumption is below zero.

Today’s-money value

The expected future balance discounted by the inflation assumption to show approximate present-day purchasing power.

Estimated fee drag

The difference between the expected projection with the entered annual fee and the same projection with fees set to zero.

Growth share

The percentage of the expected ending value produced by projected growth rather than contributions.

Chart and annual table

The chart shows the direction of the three scenarios. The table provides the calculated balance and cumulative contributions at the end of each year.

Best way to compare: change one field at a time. For example, hold the return constant while testing £100, £250 and £500 monthly contributions. This makes the effect of each decision easier to see.

How the Compound Interest Calculator Maths Works

Compound interest is growth applied to both the original balance and growth already accumulated. For investments, compound growth is often the more accurate description because returns vary and are not fixed interest payments.

The calculator subtracts the annual fee assumption from each scenario’s annual return, converts that net rate into an equivalent monthly rate using the selected compounding frequency, and then processes the balance month by month. Contributions are added at the beginning or end of each month according to your selection.

Net annual rate: r = scenario return − annual fee

Equivalent monthly rate: i = (1 + (r ÷ n))n ÷ 12 − 1

End-of-month contributions: FV = P(1 + i)m + PMT × (((1 + i)m − 1) ÷ i)

Beginning-of-month contributions: multiply the contribution part by (1 + i)

FV is future value, P is the starting balance, r is the net annual rate written as a decimal, n is the selected number of compounding periods per year, i is the equivalent monthly rate, m is the number of months and PMT is the monthly contribution. When the monthly rate is zero, the result simplifies to the starting balance plus all contributions. The live calculator performs the calculation month by month, which also handles beginning-of-month contributions directly.

This is a smooth mathematical model. It does not simulate market volatility, sequence-of-returns risk, taxes, changing contributions, missed months, dealing costs or withdrawals.

Monthly Contributions and Trader-to-Investor Mode

In Standard Investor mode, the monthly contribution is added directly to the long-term portfolio. A larger contribution does not guarantee a particular outcome, but it is an input you can control more directly than future returns.

Trader-to-Investor mode calculates the monthly investment as:

Trading profit × percentage withdrawn × percentage invested + additional monthly investment

For example, average monthly trading profit of £1,000, with 50% withdrawn and 50% of that withdrawal invested, redirects £250. Adding £100 from other income produces a £350 monthly investment contribution.

Use a cautious average rather than a best month. Trading profits can be irregular or negative, and prop-firm rules, losses or account changes can interrupt contributions entirely. This mode models the long-term portfolio only; it does not forecast trading performance.

Fees, Inflation and the Three Projection Scenarios

The expected scenario uses the annual return you enter. The cautious scenario subtracts the selected scenario range, while the optimistic scenario adds it. The annual fee is then deducted from each scenario before the projection is calculated.

Cautious

A lower-return illustration. It is not a worst-case result and does not show the full range of possible losses.

Expected

Your central return assumption after the annual fee assumption has been deducted.

Optimistic

A higher-return illustration used to show sensitivity, not to imply that the best outcome is likely.

Inflation-adjusted

The expected future value divided by the cumulative inflation assumption to estimate today’s purchasing power.

Compound Interest Calculator (free, no sign up)

Use this free compound interest calculator with no sign-up to estimate how a lump sum, regular monthly contributions or reinvested trading profits could grow over time. It can be used for long-term investment planning, savings projections, retirement scenarios, testing different annual return assumptions, comparing contribution levels, and seeing how annual fees and inflation may affect the result.

Bookmark the main page when you want a clean calculator each time. To save one precise scenario, select Copy shareable link beneath the annual table and bookmark the copied address. The calculation inputs are stored in that URL so the same scenario can be reopened later.

Methodology, Assumptions and Independent Sources

The calculator uses standard compound-growth mathematics with user-controlled assumptions for return, fees, inflation, contribution timing and compounding frequency. It is an educational planning tool rather than financial, investment, tax or trading advice.

For further independent background, see the official Investor.gov compound interest calculator, the UK Office for National Statistics inflation information and MoneyHelper’s beginner investing guide.

These sources provide general educational context. They do not validate the return assumptions entered into this calculator or imply that a projected result will occur.

New to Trading? Explore GradTraders

This calculator may be the first GradTraders page visited by someone who is interested in investing but has not traded before. Start with education and risk before comparing accounts, funded programmes or software. The links below open the main areas of the site without requiring a purchase or sign-up.

Trading for Beginners

Start with a complete plain-English introduction to markets, brokers, platforms, risk and the practical steps before trading.

Open the Beginner Guide

Trading Guides

Explore the wider education library covering brokers, platforms, leverage, risk management and trading terminology.

Explore Trading Guides

Where Traders Invest

Continue from this calculator into guides about long-term wealth, investment accounts and using trading profits beyond trading.

Explore Long-Term Investing

Live Trading and Replays

See GradTraders document live demo analysis and the trading process without presenting it as guaranteed income.

Watch GradTraders Live

Exclusive Discounts and Updates

Check the current GradTraders partner offers and updates after completing your own research.

View Discounts and Updates

Compound Interest Calculator FAQs

What is compound interest?

Compound interest is growth earned on both the original balance and growth already accumulated. For investments, compound growth is often the more accurate term because market returns are variable rather than fixed interest payments.

How do I use this compound interest calculator?

Choose Standard Investor or Trader-to-Investor mode, enter a starting balance, monthly contribution, annual return and whole-year period, then review the scenarios and supporting results. Advanced options add fees, inflation, compounding frequency and contribution timing.

Does the calculator include monthly contributions?

Yes. Standard Investor mode adds the amount entered every month. Beginning-of-month contributions receive one additional month of potential growth compared with end-of-month contributions.

How does Trader-to-Investor mode calculate the monthly amount?

It multiplies average monthly trading profit by the percentage withdrawn and then by the percentage of withdrawals invested. Any additional monthly investment is added to that amount.

Why does the calculator show three scenarios?

The cautious, expected and optimistic scenarios show how sensitive the result is to different return assumptions. They are illustrations rather than best-case, worst-case or guaranteed forecasts.

How are fees and inflation applied?

The annual fee is subtracted from each scenario’s annual return before growth is calculated. Inflation is applied separately to the expected ending balance to estimate its approximate value in today’s money.

Does this calculator predict actual investment returns?

No. It produces smooth mathematical projections from the assumptions entered. Real investments can rise, fall or lose money, and taxes, volatility, dealing costs, changing contributions and withdrawals can materially change the outcome.

Which compounding frequency should I choose?

For a general long-term investment projection using an expected annual return, choose Annually. Choose Quarterly, Monthly or Daily only when the account or product documentation states that growth or interest is credited and reinvested at that frequency.

Do I need to sign up, and can I save a calculation?

No sign-up, account or email address is required. Bookmark the main page for future use, or select Copy shareable link to save the inputs for one particular scenario in the page URL.