How to calculate return on investment (ROI), step by step

Learning how to calculate return on investment sounds like it should need one formula, and it does — the formula fits on an index card. The mistakes I see are never in the division; they are in what people leave out of the two numbers before they divide. A forgotten dividend here, closing costs ignored there, and two investments that look identical turn out to be nothing alike. So I will work three examples end to end — a stock, a rental property’s down payment, and a small-business purchase — showing every input, including the ones that are easy to forget, and then annualise each one, because an ROI without a time span is only half an answer.

The formula, in five steps

ROI = (final value − total cost) ÷ total cost × 100, expressed as a percentage. Worked properly, it goes like this:

1. Total your real cost. Not just the sticker price — include commissions, closing costs, transfer taxes and anything you spent to get in.
2. Total your final value. The sale price (or current value) plus every dollar the investment paid you along the way: dividends, interest, net rent, distributions.
3. Subtract to get the gain: final value − total cost.
4. Divide the gain by the total cost and multiply by 100. That is your ROI.
5. Write down the years. A 40% ROI over two years and over twenty years are different investments wearing the same number. Step five — annualising — is covered right after the first example.

Example 1: a stock, with its dividends counted

I buy 100 shares at $48: $4,800, and assume no commission. Over three years the stock pays me $420 in dividends. I then sell at $61 a share: $6,100. Final value is $6,100 + $420 = $6,520. Gain: $6,520 − $4,800 = $1,720. ROI = 1,720 ÷ 4,800 = 35.83%. Now watch the classic error: forget the dividends and the same investment “returns” ($6,100 − $4,800) ÷ $4,800 = 27.08%. Nothing changed except the bookkeeping — and the answer moved by almost nine points. Dividends are part of the return. Always.

The missing ingredient: time (annualising ROI)

ROI says how much; it is silent on how long. The fix is the annualised return, also called CAGR: (final value ÷ total cost)^1/years − 1. For the stock: ($6,520 ÷ $4,800)^1/3 − 1 = 10.75% a year. The same 35.83% ROI stretched over ten years instead of three would annualise to just 3.11% a year. Whenever you compare two ROIs, annualise both first — it is the only fair comparison, and it is the rate you can then feed into the investment calculator to project what happens if the performance repeats.

Example 2: a rental property — ROI on the down payment

Property investors usually measure ROI against the cash they actually committed, which means leverage enters the picture. Here are the full assumptions, nothing hidden:

Rental example assumptions, stated in full. Figures before income tax; selling costs handled separately below.

Total value back: $119,752.44 of equity + $9,000 of net rent = $128,752.44. Gain: $128,752.44 − $66,000 = $62,752.44. ROI = $62,752.44 ÷ $66,000 = 95.1% over five years, which annualises to 14.30% a year. Now the honesty pass. Sell the property and a typical 6% in selling costs takes $20,665.13 off the top: value back falls to $108,087.31, ROI to 63.8%, annualised 10.37% — before income tax. And notice the leverage: that headline 95.1% is a return on $66,000 of cash, not on the $300,000 asset; measured against the full price plus closing costs, the same gain is a 20.5% return. Leverage magnifies ROI on cash in both directions — a falling market would have multiplied the loss the same way.

Example 3: a small-business purchase, and when ROI needs a partner

A business spends $25,000 on equipment. The machine adds $9,000 a year of profit for four years, then is sold for $8,000. Total value back: (4 × $9,000) + $8,000 = $44,000. Gain: $19,000. ROI = $19,000 ÷ $25,000 = 76%. But here ROI has a blind spot: the money arrived along the way, not in one lump at the end, and a dollar in year one is worth more than a dollar in year four. Spreading the gain evenly — the naive annualised figure — gives 15.18% a year, which understates it. The measure built for uneven cash flows is the internal rate of return (IRR): the single rate that makes the inflows, correctly timed, equal the $25,000 outlay. For this machine the IRR is about 24%. Rule of thumb: the more the cash arrives in instalments rather than at the end, the more IRR tells you that plain ROI cannot.

The four ROI traps

• Leaving costs out. Fees and closing costs are part of the cost. Omitting them flatters every ROI you compute.
• Forgetting the cash it paid you. Dividends, interest and rent are return. The stock example moved nine points on this alone.
• Comparing ROIs across different time spans. Annualise first, compare second — 35.83% is 10.75% a year over three years and 3.11% over ten.
• Ignoring leverage and risk. A 95.1% ROI on a down payment is a leveraged figure; the same deal unleveraged returns far less, and a price fall would have cut the other way just as hard.

And yes, ROI can be negative: put $2,000 in and take $1,700 out and the formula gives ($1,700 − $2,000) ÷ $2,000 = −15%. The formula does not judge; it reports.

Method: all figures computed for this article from the ROI and compound annual growth rate formulas; the mortgage payment and remaining balance from the standard amortisation formula; the IRR found by solving the cash-flow equation for the equipment example. Examples are simplified illustrations with assumptions stated in full — not investment advice.