How to Calculate ROI: Formula, Examples, and Common Pitfalls

What Is ROI?

Return on Investment (ROI) is one of the most widely used financial metrics. It measures the efficiency of an investment by comparing the gain (or loss) to its cost. ROI is expressed as a percentage, making it easy to compare investments of different sizes and types — from a £5,000 marketing campaign to a £500,000 real estate purchase.

The ROI Formula

Where Net Profit = Total Return − Cost of Investment. A positive ROI means you earned more than you spent. A negative ROI means you lost money.

Step-by-Step Example: Marketing Campaign

Suppose you spend £8,000 on a paid advertising campaign. The campaign generates £22,000 in attributable revenue and the cost of goods sold on those sales is £10,000.

1. Calculate net profit: £22,000 revenue − £10,000 COGS − £8,000 ad spend = £4,000
2. Divide net profit by investment: £4,000 ÷ £8,000 = 0.50
3. Multiply by 100: 0.50 × 100 = 50% ROI

For every pound invested in advertising, you earned £1.50 back (your original £1 plus £0.50 profit). Use the ROI Calculator to run this calculation with your own numbers.

ROI for Different Investments

Marketing & Advertising

Marketing ROI measures whether campaigns generate more revenue than they cost. When calculating, include all associated costs: ad spend, agency fees, creative production, software tools, and staff time. Attribute revenue carefully — a common pitfall is crediting an ad campaign for sales that would have happened anyway (organic demand).

Real Estate

For a property investment, the calculation includes purchase price, renovation costs, ongoing maintenance, and taxes as the investment cost. The return includes rental income and/or the sale price minus the purchase price. A house bought for £200,000 with £30,000 in renovations and sold for £280,000 yields: (£280,000 − £230,000) ÷ £230,000 × 100 = 21.7% ROI. This does not account for holding time — a 21.7% return over five years is very different from the same return over one year.

Equipment & Capital Expenditure

A manufacturer buying a £50,000 machine that saves £15,000 per year in labor costs has an annual ROI of 30%. The payback period — how long until the machine pays for itself — is £50,000 ÷ £15,000 = 3.33 years. ROI is useful for comparing alternative equipment purchases: the machine with the highest ROI delivers the best return per pound invested.

Stock Market

For stocks, ROI includes both capital gains (price increase) and dividends received. If you buy shares for £10,000, receive £400 in dividends, and sell for £11,500: net profit = £11,500 + £400 − £10,000 = £1,900. ROI = £1,900 ÷ £10,000 × 100 = 19%.

Limitations of ROI

ROI is powerful but has blind spots. Being aware of them prevents poor decisions:

• Time is ignored. A 50% ROI over one year is excellent. A 50% ROI over ten years is mediocre (roughly 4.1% per year). Standard ROI does not factor in how long the investment takes to deliver returns.
• Risk is invisible. A 20% ROI from government bonds and a 20% ROI from a speculative startup are not equivalent. ROI says nothing about the probability of achieving the return.
• Opportunity cost is excluded. Every pound invested in one project is a pound not invested elsewhere. An ROI of 15% looks good until you realize the alternative investment offered 25%.
• Cash flow timing matters. Two investments may have the same total ROI, but one returns cash in year one while the other returns cash in year five. The earlier cash flow is more valuable (time value of money).

Annualized ROI

To compare investments held for different time periods, convert to annualized ROI:

Example: An investment returns 50% over 3 years. Annualized ROI = (1.50)^(1/3) − 1 = 14.5% per year. This makes it directly comparable to an investment that returned 12% in one year.

ROI vs Other Metrics

Calculate Your ROI

Use the ROI Calculator to find your return on any investment. For broader profitability analysis, try the Profit Calculator or the Break-even Calculator to determine how many units you need to sell before an investment becomes profitable.

If you are evaluating the profitability of a product rather than an investment, see our guide on How to Price a Product for practical pricing formulas and strategies.