SEO vs PPC Crossover Calculator

What this number means

The crossover month is the first month in which cumulative SEO profit catches up with cumulative PPC profit. Before that point, PPC has earned more in total; after it, SEO pulls ahead and the gap typically keeps widening, because monthly SEO profit at full ramp exceeds the flat monthly PPC profit.

With the default inputs, crossover lands in month 16: the 24-month cumulative net is $348,000 for SEO versus $300,000 for PPC. The winner label simply names the higher 24-month cumulative total. Use this to answer the practical question: should we keep spending on ads while SEO ramps? The two charts show the cost of the ramp period and the payoff after it.

The formula

In plain English: PPC profit is identical every month — ad spend buys clicks, clicks convert at your conversion rate, each customer contributes value times margin, minus the spend. SEO profit starts near zero and rises linearly until rankings stabilize, then holds flat at full-ramp profit.

• PPC monthly net = (Monthly spend / Avg CPC) x Conversion rate x Customer value x Gross margin - Monthly spend
• SEO clicks in month m = Full-ramp clicks x min(m / Ramp months, 1)
• SEO monthly net = SEO clicks x Conversion rate x Customer value x Gross margin - Monthly SEO cost
• Crossover = the first month m where cumulative SEO net is greater than or equal to cumulative PPC net, and cumulative SEO net is above zero

All money figures are monthly unless labeled cumulative. Percentages are entered as whole numbers (3 means 3%).

Worked example

A B2B software company spends $5,000/month on PPC at a $3.00 average CPC with a 3% conversion rate. That buys 1,667 clicks and 50 customers a month. At $500 customer value and 70% gross margin, PPC nets $12,500/month — $300,000 over 24 months, flat.

The same company invests $3,000/month in SEO, expecting 2,000 organic clicks per month once rankings stabilize after a 9-month linear ramp. At full ramp SEO nets $18,000/month. The early months run at a loss (month 1 nets -$667), but by month 16 cumulative SEO profit overtakes PPC and finishes the 24 months at $348,000 — $48,000 ahead. The operational takeaway: keep PPC funded through month 16 to cover the ramp, then reallocate that spend.

Assumptions and limitations

• The linear ramp is a simplification. Real rankings arrive in steps — plateaus, then jumps after content pushes or core updates — not a straight line. Treat the ramp as a planning average.
• One conversion rate for both channels. Organic visitors often convert at a different rate than paid visitors. If you have channel-specific data, adjust the rate accordingly.
• Flat PPC economics. CPCs drift with auction competition, seasonality, and Quality Score changes; the model holds them constant for 24 months.
• No assisted conversions or brand lift. SEO frequently lifts branded search and direct traffic, which this model does not credit to SEO.
• 24-month horizon with no discounting. Future profit is not discounted to present value, which slightly flatters the slower channel.
• All outputs are planning estimates, not guarantees of performance.