C4 · Economics & metrics · ratio

GTM Magic Number

Also: Magic Number

Definition. The conventional SaaS Magic Number is 4 × the change in quarterly subscription revenue divided by prior-quarter S&M spend. An ARR-change/S&M ratio is a separate variant with different timing. Both are aggregate diagnostics affected by acquisition, expansion, churn, recognition and cost allocation; neither measures causal marginal ROI.

ratio convention established; causal and payback interpretations require additional assumptions Last updated 2026-06-18 Source: Formula convention: https://chartmogul.com/saas-metrics/magic-number/. Score bands below are historical practitioner heuristics, not current empirical guarantees.

Formula

GTM Magic Number ratio

Magic_{Q} = \frac{4 ( Revenue _{Q} - Revenue _{Q - 1} )}{S&M _{Q - 1}}

Plain English: Magic Number = 4 × (subscription revenue this quarter - last quarter) / S&M spend last quarter

Notation: Magic_Q = 4×(Revenue_Q - Revenue_{Q-1})/S&M_{Q-1}; ARR-change variant = (ARR_Q - ARR_{Q-1})/S&M_{Q-1}

Benchmark by stage

Source: Formula convention: https://chartmogul.com/saas-metrics/magic-number/. Score bands below are historical practitioner heuristics, not current empirical guarantees.

Stage	GTM Magic Number	Notes
Warning	< 0.5	Practitioner heuristic band; verify numerator convention, cohort economics and marginal incrementality before changing spend.
Acceptable	0.5 – 0.75	Practitioner heuristic band; verify numerator convention, cohort economics and marginal incrementality before changing spend.
Good	0.75 – 1.0	Practitioner heuristic band; verify numerator convention, cohort economics and marginal incrementality before changing spend.
Excellent	> 1.0	Practitioner heuristic band; verify numerator convention, cohort economics and marginal incrementality before changing spend.
Exceptional	> 1.5	Practitioner heuristic band; verify numerator convention, cohort economics and marginal incrementality before changing spend.

Naive vs corrected

Version	Formula
Naive	Mixing a quarterly recognized-revenue numerator with an ARR numerator while applying the same annualization factor, or interpreting the ratio as attributed incremental return.
Corrected	Choose and label the recognized-revenue or ARR-change variant. Annualize quarterly revenue growth by 4; do not multiply an already annualized ARR change by 4 or 12. A lag is a reporting convention, not proof that this spend caused that output.

Common errors

Applying ×12 to a quarterly revenue difference or annualizing ARR twice
Presenting net ARR change as new-logo acquisition alone
Using a mechanically chosen lag as a causal attribution rule
Comparing different recognition, margin or cost definitions
Treating a high score as sufficient evidence to increase spend

Where this sits

Part of the Economics & metrics (C4) cluster in the GTM World Model. Related to the model's "No general identity connects Magic Number to customer payback. Under a deliberately simplified ARR-new-logo variant with exactly matched acquisition cost, constant per-customer contribution margin and no churn/expansion, payback_months≈12/(ARR_variant×margin). Those assumptions do not hold automatically for the aggregate conventional ratio." equation.

cac →cac payback →burn multiple →rule of 40 →

How to cite this

@misc{shalvi_gtm_metric_magic_number_2026,
  author = {Singh, Shalvi},
  title  = {GTM Magic Number — GTM World Model Metrics},
  year   = {2026},
  url    = {https://shalvisingh.com/gtm/metrics/magic-number}
}

Singh, Shalvi. "GTM Magic Number — GTM World Model Metrics." shalvisingh.com, 2026. https://shalvisingh.com/gtm/metrics/magic-number