🚀 Investment Growth Calculator
See how your investment portfolio grows over time with regular contributions and compound returns.
See how your investment portfolio grows over time with regular contributions and compound returns.
How fast will my investments grow?
The Rule of 72 gives a quick estimate: 72 ÷ annual return = years to double. At a 7% real return, money doubles roughly every 10 years. With a $500 monthly contribution and 7% real growth, a $10,000 starting balance grows to about $250,000 over 20 years and $830,000 over 35 years.
| Year | Portfolio Value | Total Invested | Total Gains |
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How to use this calculator
Takes about 2 minutes.
- Enter your initial investment amount
- Add the annual contribution you plan to make on top
- Set the expected annual return — 7 percent is a common long-term equity assumption
- Pick the investment period in years
- Click Calculate to see your projected portfolio value, total contributions, and interest earned
Try these scenarios
Tap a scenario to load it into the calculator above.
Key concepts
Lump sum vs. drip-feed. A lump-sum invested at day one mathematically outperforms the same money drip-fed monthly, because more of it spends more time in the market. Vanguard research finds lump-sum wins roughly two-thirds of the time over a 10-year horizon. The downside: bigger short-term regret if the market drops the week after you invest.
Dollar-cost averaging. Spreading contributions monthly smooths your average purchase price and protects against bad timing. It's mathematically suboptimal but psychologically easier — and most people earn money monthly anyway.
Real vs. nominal growth. A 7% nominal return with 3% inflation is a 4% real return. The calculator can be run either way — for long-horizon planning, real returns give you a meaningful purchasing-power figure.
Sequence and volatility. Two portfolios with the same average return but different paths end up at different places because of how returns interact with contributions and withdrawals. Higher volatility erodes the compound average (the 'variance drain').
Costs compound too. A 1% annual fee on a 7% return is a 14% drag on your gross return. Over 30 years, the difference between a 0.1% index fund and a 1% active fund can be 20-25% of your final balance.
UK investors — S&P 500 via accumulation ETFs. For UK readers specifically modelling US equity exposure through VUSA, VUAG, CSPX, or SPXP inside an ISA or SIPP, the UK S&P 500 calculator applies the wrapper, OCF, and GBP/USD currency-drag maths to the same compound-growth engine.
Frequently Asked Questions
Worked example — $10,000 plus $500/month at 7% for 20 years
Picture a 35-year-old in the US who has saved $10,000 in a brokerage account and can add $500 a month from now on. They plan to invest in a low-cost S&P 500 index fund and use a 7% nominal annual return — broadly consistent with the long-run S&P 500 average reported in FRED's total return series and Shiller's century-plus dataset. They want a 20-year horizon, projecting to age 55.
The calculator iterates year by year. Year one: $10,000 grows by 7% to $10,700, then $6,000 of contributions ($500 × 12) is added, ending at $16,700. Year two takes the $16,700, grows it to $17,869, adds another $6,000, and lands at $23,869. The compound annuity formula expressed up front is FV = P(1+r)^n + C × [((1+r)^n − 1) / r], where P is principal, C is annual contribution, r is the return, and n is years. Plugging in P=$10,000, C=$6,000, r=0.07, n=20 produces a final balance of roughly $284,640 from $130,000 of total contributions and $154,640 of growth.
The interpretation is that more than half the ending balance came from market returns rather than money the saver put in — and that ratio increases with time. Push the horizon to 30 years and the projection rises to about $635,000, of which $445,000 is growth and only $190,000 is contributions. Cut the return to 5% (a stress-test real return) and 20 years yields about $237,000; lift it to 9% and you reach $345,000. The return assumption swings the answer by tens of thousands, which is why the FAQ above pushes back on aggressive default rates.
Common projection mistakes
- Using a nominal return then expressing the answer in today's money. A 7% nominal projection over 30 years includes inflation. To compare the final pot to today's prices, divide by (1+inflation)^years or subtract inflation from the return up front. Mixing the two understates how much you actually need to save.
- Ignoring fees. A 1% annual management fee on a 7% gross return is a 14% drag on net return. Over 30 years, that gap typically removes 20–25% of the projected final balance. The calculator's headline rate is gross — subtract your fund expense ratio and platform fees before entering it for a realistic figure.
- Assuming returns are smooth. The formula uses an average annual return, but real markets are lumpy. A 7% average can be -20%, +30%, +5%, -10% in consecutive years — the same arithmetic mean, very different psychological experience. Sequence risk matters most in the five years before and after you start withdrawing.
- Ignoring tax wrappers. Compounding the same $6,000/year inside a Roth IRA, ISA, or TFSA versus a taxable brokerage produces materially different end balances because dividends and realised gains are not taxed annually inside the wrapper. The order of operations matters: max the tax wrapper first.
- Treating the projection as a promise. The output is conditional on three uncertain inputs: future returns, sustained contributions, and that you don't sell during downturns. Treat it as a planning baseline to flex, not a target to anchor on.
When to use the Investment Growth Calculator
Reach for this tool when you have a portfolio and a contribution rate and you want a single ballpark figure for what it could be worth at a future date. It is the right calculator for "if I keep putting $X in for Y years at Z return, what do I get?" — the standard accumulation question. It is not the right tool for retirement adequacy (use the Retirement Savings Calculator, which works backwards from a target spending number) or for a fixed-end goal like a house deposit (use the Savings Goal Calculator, which solves for time given a target).
For decisions involving choice between investment wrappers — Roth IRA vs taxable, ISA vs General Investment Account, TFSA vs unit trust — run this calculator twice with different effective return assumptions. A reasonable shortcut is to apply a 0.5–1.0 percentage-point drag for taxable accounts to reflect annual tax on dividends and realised gains. The gap between the two projections is the value the wrapper is delivering, which often surprises savers who assumed the difference was marginal.
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