What you'll need to calculate SEO ROI
The calculator asks for eight inputs. Most of them you'll either know off the top of your head or can pull from Google Analytics in a few minutes.
- Last 12-month SEO traffic
- Your total organic sessions over the past year. Pull this from GA4 filtered to the organic channel.
- Baseline monthly SEO traffic
- Your average monthly organic sessions before the project starts. This is the starting point for all projections.
- Do-nothing growth rate
- How much your traffic would grow anyway, without the SEO project, based on your historical trend. It stops you crediting SEO with growth that was always going to happen.
- Target SEO growth rate
- The year-on-year traffic growth your agency is projecting. This should come directly from their proposal.
- SEO conversion rate
- The percentage of organic sessions that convert to a sale or lead, from GA4 filtered to organic traffic.
- Customer LTV
- The lifetime value of a customer. If repeat purchases are rare, your average order value works fine.
- Gross margin
- Revenue minus cost of goods, expressed as a percentage.
- Total SEO project cost
- Everything: agency fees, content production, tools, and your own time if it is significant.
What you get back
It starts with the traffic picture: your do-nothing projection and your SEO-powered target. The difference between the two is your incremental traffic, the sessions the project actually needs to deliver to justify the investment.
From there it works out the extra conversions, revenue and gross profit the project brings in, deducts your project cost to show net return, and calculates ROI for Year 1 and Year 2. Year 2 assumes the traffic you built in Year 1 keeps growing at your do-nothing rate with no additional SEO spend, so the original investment keeps delivering.
- Traffic vs. baseline (M1–M12). Months 1 and 2 assume no SEO-driven growth, since early work is mostly technical. From month 3, growth builds linearly to month 12.
- Monthly gross profit lift (M3–M12). The estimated increase in gross profit each month attributable to the project.
- Cumulative return vs. cost. Cumulative gross profit plotted against total cost. The point where the lines cross is your break-even month.
How to read the results
The calculator gives you a projection, not a guarantee. SEO results depend on execution, competition, algorithm changes and factors neither you nor your agency can fully control.
Use the outputs as a range, not a verdict. Switch to the conservative scenario, which halves the projected traffic growth: if the numbers still look strong, the project has a reasonable risk profile. If break-even only works when everything goes to plan, that's worth knowing before you sign.
This calculator is provided for informational purposes only. We are not responsible for outcomes resulting from its use.