ROI (Return on Investment)

Whether a product investment will pay back, how fast, and by how much.

When to use this

You're deciding whether to fund a project with a clear cost and a measurable gain. You can name the gain in dollars (saved CAC, added revenue, reduced support load that actually reduces headcount). You'll commit to measuring the gain after launch. You'd actually kill the project if the math came out badly.

Limits

Pure-research bets where the gain is unknowable up front. Defensive moves you'd do regardless of the math (security fixes, compliance work, table-stakes parity features). Small fast decisions where the analysis costs more than the decision itself. For mandatory work, use cost and benefit estimates to compare implementation options rather than pretending the score decides whether the work is needed.

Inputs

Cost: Total fully-loaded cost. Engineering, design, PM, QA time. Plus any infra, tools, or vendor spend. Use salary, benefits, and allocated overhead from your cost data.
Gain: Expected dollar benefit over a defined window (usually 12 months). Be specific about whether this is revenue, saved cost, or both.
Time horizon: Usually 12 months. Choose a horizon that fits the investment and show when costs and benefits occur.

The math

ROI (%) = (gain - cost) / cost x 100
Payback period = cost / monthly_gain
Benefit-cost ratio = gain / cost

ROI is the headline number. Payback tells you when the money comes back. Benefit-cost ratio is a quick gut check ("for every $1 in, $X out").

A worked example

Your team is debating whether to build a self-serve onboarding flow.

Cost: This simplified example includes engineering labor only; assume no additional costs for the arithmetic below.

3 engineers x 8 weeks
Loaded cost: $4,000/week per engineer
Total: 3 x 8 x $4,000 = $96,000

Gain:

Cuts acquisition cost by $80 per new paying self-serve customer
~600 new paying self-serve customers per month
Monthly saved CAC: 600 x $80 = $48,000
12-month gain: $48,000 x 12 = $576,000

The math:

Payback = $96,000 / $48,000 = 2 months
12-month ROI = ($576,000 - $96,000) / $96,000 = 500%
Benefit-cost ratio = $576,000 / $96,000 = 6.0

The estimate gives 2-month payback and 500% ROI. The 600 new customers/month and $80 saved per customer are forecasts, so check those assumptions and any omitted costs before committing. A 50% miss on either input still leaves you with a positive ROI in this case, which is the actual stress test worth running.

In PM Toolkit

The calculator shows ROI alongside payback and benefit-cost ratio. Use its what-if controls to compare assumptions. A positive result depends on the costs and benefits you included.

Common mistakes

Ignoring timing. Compare payback, risk, and the benefit period alongside ROI.
Using one gain estimate. Test a lower-benefit case and state its assumptions.
Ignoring alternatives. Compare the project with other uses of the same resources.
Calling saved hours cash savings. Freed time is capacity; cash savings require reduced spending. Explain how you value any redeployed capacity.
Choosing a longer horizon only to improve the result. Use a period appropriate to the investment and consider discounting future cash flows.
Skipping measurement. Record how you will compare actual costs and benefits with the forecast.