Calculate contribution after variable costs
For an online shop, the scenario starts with extra visits. Multiply them by the purchase rate, average order value and contribution margin. Then subtract the monthly SEO costs. ROI is that net contribution divided by the SEO costs, multiplied by 100%.
Contribution margin is the share of revenue remaining after the variable costs included in your calculation. These might include purchasing, payment and shipping costs. Use a consistent definition and exclude VAT from all amounts. If returns or extra customer support costs are excluded, note this alongside the scenario.
This model evaluates a chosen situation. It does not predict how much extra traffic a Google position will bring. Enter a supported assumption, then explore how sensitive the result is to changes.
ROI = (extra contribution − SEO costs) ÷ SEO costs × 100%
An e-commerce example
Suppose you assume 1,000 extra visits per month, a 2% purchase rate, an average order value of €150 and a 40% contribution margin. That produces 20 orders, €3,000 in revenue and €1,200 in contribution before SEO costs.
With monthly SEO costs of €499, this scenario leaves €701. The calculated ROI is approximately 140.5%. That figure describes these inputs, not the expected performance of cognito or any other agency.
The expected contribution per extra visitor is €1.20 here: 2% × €150 × 40%. Covering €499 requires 416 extra visits, rounded up. That is the break-even point under the same assumptions.
| Purchase rate | Contribution from 1,000 visits | After €499 in SEO costs |
|---|---|---|
| 1% | €600 | €101 |
| 2% | €1,200 | €701 |
| 3% | €1,800 | €1,301 |
Service businesses need one extra step
An enquiry is usually not yet a sale. Add the percentage of enquiries that become customers. Then use the average contribution per new customer after variable delivery costs. This avoids counting every contact form as full revenue.
Example: 1,000 extra visits at a 2% enquiry rate produce 20 enquiries. If 25% become customers, that is an average of five new customers. At €500 contribution per customer, the extra contribution is €2,500. Subtract the SEO costs for the same period.
Use a suitable evaluation period for long sales cycles. September enquiries may become customers later. Record that delay and do not assess a month with open quotes as though every enquiry was lost. Account for capacity too: extra demand you cannot fulfil has a different value.
Include all relevant SEO costs
An agency invoice is often only part of the investment. Consider your own time, technical changes, product photography and paid software. Spread one-off costs over the period you want to assess and document how you do it.
If you pay for a subscription annually in advance, divide the annual total by twelve for a monthly scenario. The actual payment is still made annually. At cognito, €3,229.20 per year is equivalent to €269.10 per month for calculation purposes. For Plus, €5,389.20 per year is equivalent to €449.10 per month.
The website price is a separate one-off cost. Do not leave it out of an ROI calculation based only on the subscription if the website is part of the investment being assessed.
View current subscriptions and website pricesCompare the scenario with actual results
Save your scenario inputs and compare them later with measured visits, enquiries or orders. Google Analytics lets you record important actions as key events. Check the setup before drawing conclusions from conversion data.
Account for seasonality, brand campaigns, returning customers and changes to your offer. Growth in organic traffic is not automatically caused entirely by the latest SEO change. Explain what the evidence supports and where assumptions remain.
Change one input at a time to see what drives the result. With a low margin, better product selection may matter more than extra traffic. With many enquiries but few sales, the fit between the page and service may need attention.
Frequently asked questions
Does a positive calculation guarantee results?
No. The calculator applies your assumptions. It does not estimate future rankings, visits or customers, and includes only the costs you enter.
What if I do not know my margin or conversion rate?
Use several clearly labelled scenarios and collect the missing data. One optimistic number is less useful than a range with explained assumptions.
