How to Calculate Return on Investment and What the Number Actually Tells You

The Basic Formula: What You Invested Versus What You Got Back

Return on Investment (ROI) is the percentage gain or loss on money you put into something. The formula is straightforward: subtract what you started with from what you ended with, divide by what you started with, then multiply by 100 to get a percentage.

If you invested $1,000 in a stock and sold it for $1,200, your gain is $200. Divide $200 by your original $1,000, and you get 0.20. Multiply by 100, and your ROI is 20%. If you sold for $800 instead, your loss is $200, your ROI is −20%.

The formula works the same way whether you are measuring a single stock, a mutual fund, a rental property, or a business investment. The math does not change. What changes is what you include in "what you started with" and "what you ended with"—and that is where most people run into trouble.

Key Takeaways

• ROI is calculated by dividing your profit or loss by your initial investment and multiplying by 100 to express it as a percentage.
• You must include all costs—trading fees, taxes, maintenance, insurance—in your calculation, or your ROI will be misleadingly high.
• ROI does not account for time, so a 50% return over one year is very different from a 50% return over ten years, even though the math is identical.
• Annualized ROI adjusts for the length of time you held an investment, making it possible to compare investments you held for different periods.
• ROI works best for comparing similar investments over similar timeframes; comparing a stock held one year to a rental property held five years requires additional context.

What Counts as "What You Invested"

Your initial investment is not just the purchase price. It includes every dollar that left your pocket to make the investment happen and keep it running.

For a stock purchase, this means the share price plus any trading commission your broker charged. For a rental property, it includes the down payment, closing costs, inspection fees, and any repairs needed before you could rent it out. For a mutual fund held in a taxable account, it is the amount you deposited.

If you add money to an investment over time—say you buy $1,000 of a stock, then buy another $500 six months later—your calculation becomes more complex. The simplest approach is to use your total invested amount ($1,500) and measure the return on that total. A more precise method, called the money-weighted return, accounts for when each deposit happened, but most individual investors use the simpler version.

What Counts as "What You Got Back"

Your ending value includes the sale price or current market value, minus any costs to sell or withdraw. If you sold a stock for $1,200 but paid a $10 trading commission, your net proceeds are $1,190.

For investments that pay income—dividends from stocks, interest from bonds, rent from property—you have a choice. You can include that income in your ending value (which shows your total return), or you can calculate ROI on price appreciation alone (which shows only the gain from the investment rising in value). Most investors care about total return, so include the income.

Taxes are the tricky part. If you sold an investment in a taxable account and owed capital gains tax, that tax reduces what you actually kept. Some investors calculate ROI before taxes (the "pre-tax return") and some after (the "after-tax return"). For comparing investments, after-tax is more honest, because it shows what actually stayed in your pocket. But if you are comparing your results to a published benchmark—like the S&P 500 index—use pre-tax, because benchmarks are published pre-tax.

Why Time Matters: Annualized Return

ROI as a simple percentage hides a critical piece of information: how long you held the investment. A 20% return over one year is exceptional. A 20% return over ten years is modest. The same number means completely different things.

To make investments comparable across different holding periods, use annualized return. This converts any return into an equivalent yearly rate, as if you earned the same percentage every single year.

The formula is: (Ending Value ÷ Beginning Value) ^ (1 ÷ Number of Years) − 1, then multiply by 100. If you invested $1,000 and it grew to $1,610 over five years, your annualized return is approximately 10% per year. You did not earn exactly 10% each year—the actual path was lumpy—but 10% per year is the equivalent steady rate.

When you see investment returns quoted in news articles or fund prospectuses, they are almost always annualized. This is why a fund that returned 50% in a single year looks spectacular, but a fund that returned 50% over ten years looks ordinary.

Costs That Shrink Your Real ROI

The ROI formula is simple, but the number it produces is only as honest as the inputs. Many investors calculate ROI and forget to subtract costs that ate into their return.

For stocks and mutual funds, these costs include trading commissions, bid-ask spreads (the difference between what you pay to buy and what you receive to sell), and expense ratios (the annual percentage fee the fund charges). A fund that returned 12% before fees but charges 1% per year in expenses actually delivered 11% to you.

For real estate, costs include property tax, insurance, maintenance, vacancy periods when the property did not generate rent, and any capital improvements you made. If a rental property appreciated $50,000 over five years but you spent $15,000 on repairs and taxes, your net gain is $35,000, not $50,000.

For any investment, if you held it in a taxable account (not a retirement account), subtract the taxes you owed on gains or income. This is the after-tax ROI, and it is the number that matters for your actual wealth.

Comparing Investments Using ROI

ROI is useful for asking: "Did this investment beat my other options?" But the comparison only works if you are measuring the same thing.

Comparing the ROI of two stocks you held for the same period is straightforward. Comparing a stock you held one year to a bond you held five years requires annualized returns. Comparing a stock (which you can sell instantly) to a rental property (which takes months to sell) requires you to think about liquidity—how quickly you can turn it back into cash—as a separate factor from return.

ROI also does not account for risk. A stock that returned 30% in a year might have swung up and down wildly, while a bond that returned 4% was stable the whole time. The 30% looks better on paper, but the path to get there was much rougher. For serious comparison, you would want to look at risk-adjusted returns, but that is beyond the scope of ROI alone.

Common Mistakes When Calculating ROI

The most common mistake is forgetting to include all costs. Investors often calculate the gain on the purchase and sale price, then claim that as their ROI, without subtracting trading fees, taxes, or maintenance. This makes the return look better than it actually was.

The second mistake is comparing returns across different time periods without annualizing. A 40% return over four years sounds worse than a 15% return over one year, but annualized, the four-year return is about 8.8% per year, while the one-year return is 15% per year. The one-year investment actually performed better, but you would not know it from the raw numbers.

The third mistake is including unrealized gains (the current value of an investment you still own) in ROI without acknowledging that the number could change. If you own a stock worth $1,500 that you bought for $1,000, your unrealized ROI is 50%. But you have not sold it yet, so that 50% is not locked in. Market prices move.

Frequently Asked Questions

How do I calculate ROI if I added money to an investment over time?

Use your total amount invested as the denominator. If you invested $1,000, then $500 six months later, and the total is now worth $2,000, your total gain is $500 and your ROI is 500 ÷ 1,500 = 33%. For a more precise calculation that weights the timing of deposits, use money-weighted return, but most individual investors use the simpler total-invested method.

Should I calculate ROI before or after taxes?

After-tax ROI shows what you actually kept, so it is more useful for personal decisions. Pre-tax ROI is better for comparing your results to published benchmarks like the S&P 500, which are reported pre-tax. Calculate both if you want the full picture.

What is the difference between ROI and annualized return?

ROI is the total percentage gain or loss over the entire holding period. Annualized return converts that into an equivalent yearly rate, making it possible to compare investments you held for different lengths of time. A 20% ROI over five years is about 3.7% annualized.

Does ROI account for risk?

No. ROI measures only the return, not how volatile or risky the path to that return was. Two investments with the same ROI could have very different risk profiles. For a fuller picture, look at volatility or standard deviation alongside ROI.

Can I use ROI to compare a stock to a rental property?

You can calculate ROI for both, but you are comparing different things. A stock is liquid (you can sell it in minutes), while a property takes months to sell. A stock generates returns through price appreciation and dividends; a property through rent and appreciation. ROI is useful for each individually, but comparing the two requires thinking about liquidity, effort, and tax treatment as separate factors.