ROI: What It Is, How to Calculate It, and Why It Can Lie to You

ROI gets thrown around constantly. “This stock had a 40% ROI!” “Our marketing campaign had a 300% ROI!” It sounds impressive, but without context, the number is almost meaningless.

Let me explain what ROI actually measures, how to calculate it properly, and — more importantly — where it falls short.

The Basic Formula

Or, equivalently:

That's it. What you gained minus what you spent, divided by what you spent. Expressed as a percentage.

Real Examples (Not $10,000 at 5%)

Stock investment: You bought 50 shares of a tech company at $100 each ($5,000 total). Two years later, the stock is at $130 per share, so your position is worth $6,500.

ROI = (($6,500 - $5,000) / $5,000) × 100 = 30%

Sounds solid. But wait — was that 30% over one year or five? That matters enormously, which brings me to the next point.

Side business: You drop $12,000 on equipment and supplies for a woodworking side hustle. Over the year, you bring in $18,000 in revenue but spend another $2,500 on materials and booth fees at craft shows.

Net Profit = $18,000 - $12,000 - $2,500 = $3,500

ROI = ($3,500 / $12,000) × 100 = 29.2%

Not bad for a first year. But this doesn't account for the hours you spent building furniture on weekends — your labor has value too.

Facebook ads: You spend $1,800 on ads for your online store and they generate $7,200 in direct sales.

ROI = (($7,200 - $1,800) / $1,800) × 100 = 300%

A 300% ROI looks incredible. And it might be — but make sure you're not counting sales that would've happened anyway. Attribution is the hardest part of marketing ROI.

The Missing Ingredient: Time

A 30% return in one year is fantastic. A 30% return over ten years? That's barely keeping pace with inflation. Simple ROI doesn't account for time at all, which is why you need annualized ROI when comparing different investments.

Where n is the number of years.

So a 50% ROI over 3 years becomes: (1.50^1/3 - 1) × 100 = 14.5% per year. Still good, but a lot less flashy than “50% ROI.”

Our ROI calculator computes both simple and annualized ROI for you, so you can compare apples to apples.

What Counts as a “Good” ROI?

It depends on what you're investing in and what risk you're taking:

• S&P 500 (stock market average): historically about 10% per year. If you're beating this consistently, you're outperforming most professionals.
• Rental property: 8-12% annual ROI including appreciation, but way more work than clicking “buy” on a brokerage app.
• Small business: most entrepreneurs aim for 15-30%+ to justify the risk and the sweat equity.
• High-yield savings account: 4-5% right now. Essentially zero risk, and honestly not a bad floor to compare against.

Where ROI Misleads You

ROI is popular because it's simple. But simplicity comes with blind spots:

• It ignores the time value of money. A dollar today is worth more than a dollar five years from now. ROI treats them the same.
• It doesn't measure risk. A 30% ROI on a crypto gamble is not “better” than a 10% ROI on Treasury bonds. Risk-adjusted returns are what actually matter.
• It misses ongoing costs. If you buy a rental property, ROI based on purchase price and rent doesn't capture maintenance, property taxes, insurance, and vacancy.
• It can be gamed. Companies sometimes calculate marketing ROI in ways that make the numbers look better than reality.

Related Calculators

• ROI Calculator — Calculate simple and annualized ROI
• Compound Interest Calculator — See how investments grow over time
• Savings Calculator — Plan your savings growth
• Break Even Calculator — Find when an investment becomes profitable