How do I calculate SEO ROI?

The basic formula is ROI = (gain from SEO − cost of SEO) ÷ cost of SEO. The hard part is estimating the gain honestly. Build it up step by step:

1. Baseline: current organic sessions, conversions and conversion rate from GA4.
2. Value: gross profit per conversion, not revenue, so the ROI reflects what you actually keep.
3. Uplift: a realistic range for extra organic sessions once the work takes effect, informed by keyword research and your competition.
4. Ramp-up: results build over months, so model a gradual increase rather than instant gains.
5. Cost: the full monthly investment, including agency fees, content, tools and internal time.

Two outputs are especially useful. The payback month tells you when cumulative profit covers cumulative cost. Break-even growth tells you how much extra traffic you need just to cover the investment; if that looks unrealistic for your site, reconsider the scope or the budget.

The SEO ROI Calculator models both, lets you change every assumption and shows its formulas. Use real data from your analytics where you can, and treat the result as a range rather than a promise.