Magic Number

The SaaS Magic Number is the sales efficiency metric calculated as quarterly net new annualized recurring revenue divided by quarterly sales and marketing spend. It's often expressed with the previous quarter's S&M spend as the denominator, on the theory that current-quarter S&M produces future-quarter ARR. The metric assesses whether the company is generating revenue efficiently from its growth investment. Values above 1.0 indicate efficient growth (every dollar of S&M produces more than a dollar of net new ARR), values between 0.5-1.0 indicate moderate efficiency, and values below 0.5 indicate problematic efficiency. It is a SaaS-specific metric that complements LTV:CAC and CAC payback.

The calculation:

Basic formula:

• Magic Number = (Net New ARR in Quarter × 4) / S&M Spend in Quarter
• Net New ARR = ending ARR minus starting ARR (includes new + expansion - churn - contraction).
• The "× 4" annualizes the quarterly ARR change.

Alternative formulation (with one-quarter lag):

• Magic Number = (Net New ARR in Current Quarter × 4) / S&M Spend in Previous Quarter
• Recognizes that S&M spend creates revenue with some lag.

Benchmark interpretation:

Magic Number > 1.5: Excellent. The company is highly efficient at generating revenue from S&M investment. Should typically invest more aggressively in growth.

Magic Number 1.0-1.5: Strong. Healthy growth efficiency. Standard "good" range.

Magic Number 0.75-1.0: Acceptable. Growing but with modest efficiency. May warrant growth investment review.

Magic Number 0.5-0.75: Concerning. Inefficient growth. Investigate where S&M is going.

Magic Number < 0.5: Problematic. Significant inefficiency. Major growth investment review needed.

What Magic Number tells you and doesn't:

Tells you:

• Overall growth efficiency at the company level.
• Whether S&M investment is producing proportional revenue growth.

Doesn't tell you:

• Cohort-level CAC payback (which can vary significantly by segment).
• Whether the revenue is high or low quality (NRR composition).
• Whether the magic number is improving or declining over time (trend matters).

Magic Number vs other unit economics:

Magic Number: top-down quarterly efficiency.

CAC Payback: months for new customers to repay acquisition cost.

LTV:CAC: lifetime value to acquisition cost ratio.

All three together provide a complete unit-economics view.

What founders get wrong: Focusing on either bottoms-up unit economics (CAC, LTV) or top-down efficiency (Magic Number) in isolation, missing the picture that emerges from triangulation. The right discipline: track all three (Magic Number, CAC Payback, LTV:CAC) and investigate divergences.

Related: CAC Payback · LTV CAC Ratio · Rule of 40 · Sales Efficiency · Unit Economics

FAQ

What is the SaaS Magic Number?
A sales efficiency metric calculated as quarterly net new ARR (annualized) divided by quarterly sales and marketing spend. Assesses whether the company is generating revenue efficiently from its growth investment.

What's a good Magic Number?
Above 1.5: excellent. 1.0-1.5: strong. 0.75-1.0: acceptable. 0.5-0.75: concerning. Below 0.5: problematic. Higher Magic Number = more efficient growth = more justified investment in scaling.

How does Magic Number relate to other unit economics?
Magic Number is top-down quarterly efficiency. CAC Payback is months for new customers to repay acquisition. LTV:CAC is lifetime value ratio. All three together provide complete unit-economics view; triangulation catches what individual metrics miss.