Magic Number
A SaaS sales efficiency metric calculated by dividing the change in quarterly recurring revenue by the previous quarter's sales and marketing spend, indicating whether growth investments are paying off.
The magic number measures how efficiently sales and marketing spend converts to new recurring revenue. A magic number of 1.0 means every dollar spent on sales and marketing generates one dollar of new ARR. Above 0.75 indicates efficient growth that justifies increased investment. Between 0.5 and 0.75 suggests room for improvement in go-to-market efficiency. Below 0.5 signals that the growth engine needs significant optimization before scaling further.
The formula is: (Current Quarter ARR - Previous Quarter ARR) / Previous Quarter Sales and Marketing Spend. This normalizes growth by its cost, enabling comparison across companies and time periods. A company growing ARR by $500K per quarter on $400K of spend has a magic number of 1.25, indicating highly efficient growth.
For growth teams, the magic number guides investment decisions. When the magic number is above 0.75, it is rational to increase sales and marketing spend because each dollar generates profitable growth. When it is below 0.5, increasing spend will likely worsen efficiency, so the priority should be improving conversion rates, reducing CAC, and strengthening the product before scaling. Tracking magic number by channel reveals which acquisition sources are most efficient.
Related Terms
Growth Loop
A self-reinforcing cycle where each cohort of users generates inputs (data, content, referrals) that attract the next cohort, creating compounding growth.
Churn
The rate at which customers stop using or paying for a product over a given period, typically measured as monthly or annual churn percentage.
Activation Rate
The percentage of new signups who complete a key action (the 'aha moment') that correlates with long-term retention and product value realization.
Product-Led Growth (PLG)
A go-to-market strategy where the product itself drives acquisition, activation, and expansion through self-serve experiences rather than sales-led motions.
Viral Coefficient (K-Factor)
The average number of new users each existing user brings to the product, where a K-factor above 1.0 indicates self-sustaining viral growth.
Net Revenue Retention (NRR)
The percentage of recurring revenue retained from existing customers over a period, including expansion, contraction, and churn — where 100%+ indicates growth without new customers.