Investment Calculators

Don’t use one – use three. Run every projection at a pessimistic, moderate and optimistic rate and plan around the range rather than the middle. Long-run US stock market returns have historically fallen in the high single digits before inflation, but an average is what happened across decades, not what happens in the ten years you happen to be investing: real sequences include long flat stretches and severe drawdowns. Whatever rates you choose, the test is the same – if your plan only works at the optimistic one, it isn’t a plan. Try it in the Compound Interest Calculator.

The arithmetic is exact; the forecast is not, and the gap between those two things is where people get hurt. A calculator applies your assumptions perfectly, but change the return assumption by a couple of percentage points across a multi-decade projection and the result can differ by more than everything you contributed. What the math can’t capture is sequence risk, where a crash early in retirement damages you far more than the same crash late, along with variable contributions and the fact that nobody knows the future return. Treat every projection as a comparison tool, not a prediction of your balance.

What does investing $500 a month actually become? Compound Interest. Am I on track to retire? Retirement Planner. How much do I need to never work again? FIRE Calculator. How long will my money last if I’m drawing on it? Investment Withdrawal. What was my actual return? CAGR. What’s my real average buy price? Average Price. What are my fund fees really costing me? ETF Overlap and Fee Drag.

Your returns start earning returns, and the effect is not linear – it’s barely visible for years and then dominates everything. As an illustration rather than a projection: investing $500 a month for twenty years at an assumed 7% annual return means you contribute $120,000, and the calculator returns a balance near $260,000, so more than half the final figure was never money you put in. Extend the same assumptions to thirty years and the compounded portion grows far faster than the contributed portion. This is why starting earlier beats contributing more. Run your own numbers.

Yes – all three, and most calculators anywhere online ignore at least two of them. Inflation is the big one: a projection showing $1,000,000 in thirty years is describing money worth far less than $1,000,000 today, so run the figure through an inflation adjustment to see it in current terms. Fund fees compound against you exactly as returns compound for you, and half a percentage point a year is very large over decades – the fee drag tool shows the size of it. Tax depends on your account type and your country. Each calculator states its own assumptions.

It works out your true weighted average purchase price when you’ve bought the same holding more than once at different prices – which is most people, most of the time. Buying in three lots at different prices doesn’t give you the average of those three prices; it gives you a weighted average based on how many shares you bought at each, and the difference can be substantial if the lot sizes differ. You need the real number to know your actual breakeven, to judge whether you’re up or down, and to calculate a gain correctly at sale. Open the calculator.

All 18 are free with no account. StockEducation is currently funded by its operator. We do not currently receive revenue from brokers, investing platforms or other financial product providers. Each calculator states its formula and its assumptions openly on its own page, so you can check the math rather than take our word for it. That matters more than a review badge: a formula you can read and test yourself is verifiable by anyone, where a claim that somebody checked it is only as good as your trust in us. Where we find an error, we fix it and publish what changed in our corrections log, with the date it was corrected.

For ETFs and index funds, yes – compounding, fees, yield and cost-basis math work identically whether you hold a single stock or a fund, and the fee drag tool is particularly worth running on funds. For tax-advantaged retirement accounts the general math still applies, but these calculators don’t currently model account-specific rules like contribution limits, employer matching or the tax treatment of withdrawals, so treat a retirement projection here as a general growth estimate rather than an account-specific one.