Free Investment Calculator

Watch your money multiply over time

See exactly how compound interest works — input your savings, pick a rate, and watch decades of wealth-building unfold instantly. Then start investing with confidence.

8×
Average 30yr multiplier
72%
Returns from interest alone
7%
Historical avg market return
Live preview
10,000 invested at 7% for 20 years
£38,697
Final balance
+£28,697
Interest earned
×3.87
Money multiplier
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No data storedAll calculations local
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Instant resultsReal-time updating
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Full breakdownCharts + year tables
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19 currenciesWorks worldwide
The calculator

See your wealth grow in real-time

Your numbers

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Your results

Final balance
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Total invested
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Interest earned
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Money multiplier
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Interest share
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Contributions vs interest
Contributions50%Interest

Growth over time

Principal & contributions Interest earned

Year-by-year breakdown

Year Balance Contributed Interest (yr) Total interest Interest %
How it works

The magic of compounding, explained

Compounding is earning interest on your interest. The longer you let it run, the more dramatic the effect.

01
You invest a lump sum
Your initial capital starts earning returns immediately. Even a modest sum can grow dramatically over time.
02
Returns compound
Each period, you earn returns on your original investment plus all previously earned interest. Growth accelerates.
03
Monthly contributions
Regular contributions amplify the effect dramatically. Even a small monthly amount makes a profound difference over 20+ years.
04
Time is the multiplier
Starting 10 years earlier can more than double your final balance. Time in the market beats timing the market.
FAQ

Frequently asked questions

Everything you need to know about compound interest and how to use CompoundIQ.

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest — which only earns on the original amount — compound interest means your returns generate their own returns, creating an exponential growth effect over time. The longer you let it run, the more dramatic the snowball becomes.
Yes — 7% is widely considered a realistic long-term average for a diversified global stock market portfolio, adjusted for inflation. The S&P 500 has historically returned around 10% annually before inflation, and roughly 7% in real terms. Individual years vary wildly — some are negative, others strongly positive — but over 20+ year periods, 7% is a reasonable planning assumption. Always remember: past performance is not a guarantee of future results.
The more frequently interest compounds, the better — daily produces slightly more than monthly, which produces more than quarterly or annually. However, the practical difference between daily and monthly compounding is very small for typical investments. Far more impactful is your rate of return and how long you stay invested. CompoundIQ lets you compare all four frequencies so you can see the difference yourself.
The Rule of 72 is a quick mental shortcut to estimate how long it takes to double your money. Simply divide 72 by your annual return rate. For example: at 7% return, 72 ÷ 7 ≈ 10.3 years to double. At 10% return, 72 ÷ 10 = 7.2 years. It's a useful rule of thumb for quickly gauging the power of different return rates without a calculator.
Yes, significantly. Inflation erodes the purchasing power of your returns over time. A balance of £144,000 in 20 years is worth considerably less in real terms than £144,000 today. As a rule of thumb, subtract the inflation rate from your nominal return to get your real return. CompoundIQ includes an inflation adjustment field that shows your inflation-adjusted real value alongside the nominal balance, so you always see what your money will actually be worth.
APR (Annual Percentage Rate) is the simple annual interest rate without compounding. APY (Annual Percentage Yield) accounts for compounding within the year and is always equal to or higher than APR. For example, a 12% APR compounded monthly gives an APY of 12.68%. When comparing savings accounts or investments, APY gives you the true effective annual return — always use APY for like-for-like comparisons.
The goal calculator works in reverse. Instead of asking "how much will I have?", it asks "how much do I need to save monthly to reach a target?". Enter your target amount, a starting lump sum (optional), your expected return rate, and your time horizon. The calculator solves the standard annuity formula backwards to tell you the exact monthly contribution required. It then shows you a chart of your path to the goal, with a dashed gold line marking your target.
Yes, completely free. There is no sign-up, no account required, and no paywalled features. All calculations happen locally in your browser — no data is ever sent to a server. CompoundIQ is supported by referral commissions from investment platforms listed on the site, which is clearly disclosed in the footer. This has no influence on the calculator's results or recommendations.
Yes — in four formats. The year-by-year breakdown table can be downloaded as a CSV (for importing into any spreadsheet), a formatted Excel (.xlsx) file with two sheets and proper number formatting, or a branded PDF report with your inputs, results summary and the full table. The chart can also be saved as a high-resolution PNG image, and the results panel can be saved as a shareable PNG card.
No. CompoundIQ is an educational tool designed to illustrate how compound interest works. It does not constitute financial, investment, tax, or legal advice. The figures shown are illustrative only — actual investment returns will vary and may be negative. Always consult a qualified and regulated financial adviser before making investment decisions.
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