Compound Interest Calculator
See how your investments grow over time with the power of compounding
Investment Growth Calculator Inputs
$
The amount you are starting with (e.g., 10000). Can be 0.
$
How much you plan to add each month (e.g., 500). Can be 0.
%
The expected annual growth rate (e.g., 8 for 8%). Historical S&P 500 average is ~10%.
How many years you plan to invest (e.g., 20)
Compound interest is the process of earning interest on both your original principal and previously accumulated interest. Unlike simple interest (which is calculated only on the initial amount), compound interest causes your wealth to grow exponentially over time. Albert Einstein reportedly called it the eighth wonder of the world.
FV = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) - 1) / (r/n)]
Étape 1: Enter your initial investment amount (the lump sum you are starting with). This can be zero if you are starting from scratch.
Étape 2: Enter your monthly contribution — the amount you plan to add each month through dollar cost averaging or a systematic investment plan.
Étape 3: Set your expected annual return rate. The historical S&P 500 average is approximately 10%, though many planners use 7-8% to account for inflation.
Étape 4: Choose your investment period and compounding frequency, then click Calculate to see your projected investment growth with a full year-by-year breakdown.
What Is Compound Interest?
Compound interest is the mechanism by which your investment earnings generate their own earnings. When you invest $10,000 at 8% annual return, you earn $800 in the first year. In the second year, you earn 8% on $10,800 — that is $864. By year 20, your annual earnings alone exceed your original investment. This exponential growth is the foundation of long-term wealth building.
The key variables that determine compound growth are the principal amount, the rate of return, the compounding frequency, and most importantly — time. The longer your money compounds, the more dramatic the results. This is why an investment calculator for compound growth is one of the most important tools for anyone planning their financial future — whether you are saving for retirement, a major purchase, or working toward your financial independence number.
Dollar Cost Averaging and Compound Interest
Dollar cost averaging (DCA) — investing a fixed amount at regular intervals — is one of the most effective strategies for building wealth over time. This dollar cost averaging calculator shows how even modest monthly contributions can grow into substantial sums when combined with compound interest. A systematic investment plan of $500 per month at 8% annual return grows to over $590,000 in 25 years — even though you only contributed $150,000. Use this as a systematic investment plan calculator to model your own DCA strategy.
The advantage of dollar cost averaging is that it removes the need to time the market. By investing consistently, you buy more shares when prices are low and fewer when prices are high, naturally averaging your cost basis. Combined with compound interest, this disciplined approach has historically outperformed most active trading strategies over long time horizons.
Compound Interest for Retirement Planning
An investment calculator for retirement planning helps you answer the most important financial question: will I have enough? By projecting your current savings and contributions forward at a realistic rate of return, you can see whether you are on track to reach your financial independence number — and how adjusting your contributions or timeline changes the outcome. Think of this as your investment calculator for retirement: enter your target number, and work backwards to find the monthly contribution and return rate you need.
For those pursuing financial independence, this calculator is essential for Coast FIRE planning (where your investments grow to your target without further contributions) and Barista FIRE planning (where part-time income covers expenses while investments compound). The difference between retiring at 55 versus 65 often comes down to a few years of additional compounding.
Frequently Asked Questions About the Compound Interest Calculator
The appropriate rate depends on your asset allocation. The S&P 500 has historically returned approximately 10% annually before inflation (about 7% after inflation). A diversified portfolio of stocks and bonds typically returns 6-8%. For conservative estimates, use 6-7%. For optimistic projections, 9-10%. Always run multiple scenarios to understand the range of possible outcomes.
More frequent compounding means your interest starts earning interest sooner, which slightly increases your total return. For example, $10,000 at 8% for 20 years grows to $46,610 with annual compounding but $49,522 with daily compounding — a difference of about $2,912 (6.2% more). The effect is more pronounced at higher rates and longer time horizons.
The Rule of 72 is a quick mental math shortcut for estimating how long it takes to double your money. Divide 72 by your annual return rate to get the approximate doubling time. At 8%, your money doubles in about 9 years (72 ÷ 8 = 9). At 10%, it doubles in about 7.2 years. At 6%, about 12 years. This rule helps you quickly gauge the power of compounding at different rates.
Yes, especially for long-term planning. You can either use a "real" return rate (nominal rate minus inflation, typically 2-3%) or calculate in nominal terms and adjust the final number for inflation separately. For example, if you expect 8% nominal returns and 3% inflation, use 5% as your real return rate to see your future value in today's purchasing power.
Fat FIRE, Lean FIRE & Barista FIRE: Which FIRE Number Is Right for You?
FIRE — Financial Independence, Retire Early — comes in several flavours, each requiring a different target number. Fat FIRE targets a high spending lifestyle in retirement, typically requiring $2–5M or more. A fat FIRE calculator uses a low withdrawal rate (2–3%) applied to a large annual expense budget — for instance, spending $120,000 per year at a 3% withdrawal rate requires $4,000,000. This compound interest calculator models exactly that accumulation path: enter your target as the future value and work backwards to the required monthly contribution and timeline.
Lean FIRE targets a frugal lifestyle, typically $800K–$1.5M. A lean FIRE calculator applies the standard 4% rule to a very low annual expense figure — $30,000 per year requires just $750,000. The trade-off is a tighter spending margin and greater sensitivity to sequence-of-returns risk in the early retirement years. Barista FIRE sits between the two: you reach partial financial independence where investments cover most expenses, and part-time income (the "barista" job) covers the remainder. This approach allows an earlier retirement date at a lower investment target. Use the Barista FIRE calculator to find your exact semi-retirement number and see how many years away it is.
Coast FIRE is a milestone rather than a full retirement target: you have accumulated enough that, even without further contributions, your portfolio will compound to your full FIRE number by traditional retirement age. Use this investment calculator to find your Coast FIRE number: enter $0 as the monthly contribution, set the end date to your target retirement age, and adjust the starting balance until the final value reaches your FIRE target. That starting balance is your Coast FIRE number — the point at which you can "coast" and let compounding do the work.
Systematic Investment Plan Calculator, Lump Sum Returns & Monthly Contributions
A systematic investment plan (SIP) calculator — sometimes called a systematic investment planner — shows how regular contributions grow over time through compounding. Unlike a lump sum investment calculator, where you enter a single starting amount, the SIP approach models ongoing monthly or yearly contributions. Returns improve dramatically with regular additions because each new contribution begins compounding immediately, layer upon layer, creating an accelerating wealth curve that a one-time deposit cannot match. Use the dedicated SIP calculator if you only have monthly contributions and want a focused SIP projection with multi-currency support.
Monthly contributions are the most practical SIP scenario: if I invest $500 per month for 20 years at an 8% annual return, what will my portfolio be worth? The calculator above handles this directly — set the contribution frequency to monthly for an ongoing systematic investment plan projection, or switch to yearly to model annual bonus contributions, tax-year ISA allowances, or lump sum top-ups. Both the investment calculator monthly and investment calculator yearly inputs work the same way: each contribution is added at the end of the period and immediately begins compounding.
The lump sum investment calculator mode is most useful when you are deciding what to do with a windfall — an inheritance, a business sale, or a bonus. Here you compare the investment calculator return on a lump sum deployed immediately versus spreading that capital over time through dollar cost averaging. Research consistently shows that lump sum investing outperforms DCA in around two-thirds of historical periods, because more time in the market means more compounding. The one-third of periods where DCA wins tend to be those immediately preceding a significant market correction — making your personal risk tolerance and timeline the deciding factor.
Track Your Real Investment Growth
Projections are the first step. With Worthmap, you can track your actual portfolio growth in real time across all currencies and asset types — and get AI-powered insights to optimize your investment strategy.
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