Expansion CAC Ratio
Definition
Fully-loaded S&M plus Customer Success expense attributable to expansion divided by expansion CARR generated in the period. Per SMSB, the efficiency read on the upsell / cross-sell / land-and-expand motion. Distinct from the new-logo CAC ratio because the cost base often includes CSMs whose primary metric is retention but whose secondary metric is expansion — boards expect to see that allocation called out. Common pitfall: excluding CS comp entirely understates the true cost of expansion; including all of CS overstates it. The SMSB standard prescribes a documented allocation rule (typically tied to expansion-quota OTE share).
Why it matters
Validates the financial logic of "expansion is cheaper than acquisition" — when this is healthy, the company should bias growth investment toward post-sale; when it inverts (Expansion CAC ≥ New CAC), the expansion motion is broken and acquisition is the only available lever.
How it's calculated
Expansion CAC Ratio = (S&M + CS spend allocated to expansion in period) / (Expansion CARR generated in period). Per SMSB §Expansion CAC Ratio: allocation rule for cross-functional comp (typically split by quota share of OTE) must be documented and consistent. How to interpret it
Per SMSB convention, healthy Expansion CAC Ratio is typically 3–5× cheaper than New CAC Ratio — i.e. 0.2–0.5 when New CAC Ratio is ~1.5. Expansion CAC Ratio > 1.0 is a yellow flag (expansion costs as much as it earns); inversion vs New CAC Ratio is a red flag warranting a CS / sales-team org review.
Source
SaaS Metrics Standards Board · Expansion CAC Ratio
Metric definitions reference standards published by the SaaS Metrics Standards Board (saasmetricsboard.com). imboard is not affiliated with, endorsed by, or a member of SMSB.
Stage relevance
Typically owned by
Related KPIs
Total fully-loaded S&M spend in the period divided by the dollars of new CARR generated in the period (new-customer + expansion CARR combined). Per the SMSB standard, the headline efficiency ratio for the full sales-and-marketing motion — answers "how many cents do we spend on S&M to add one dollar of contracted ARR." Common pitfall: blending without separately reporting New CAC Ratio and Expansion CAC Ratio hides which side of the motion is driving efficiency — for a healthy SaaS company expansion CAC is usually 3–5× cheaper per dollar than new-logo CAC.
S&M expense attributable to new-customer acquisition divided by the new-customer CARR generated in the period. Per SMSB, the cleanest read on the new-logo acquisition engine's efficiency — strips out the expansion motion which has materially different unit economics. Common pitfall: failing to split AE comp time correctly between new and expansion activities — when the same AE owns both motions, an allocation rule (often the % of OTE tied to new-vs-expansion quota) is required and must be applied consistently quarter-over-quarter.
Annualized recurring revenue added during the period from existing customers — through upsell (more seats / higher tier), cross-sell (additional products), or price increases. The "farm" line of the ARR waterfall. Boards read this as the leading indicator that product-market fit has translated into product-account fit and that the post-sale motion is creating compound growth. Common pitfall: classifying contractual price-step-ups (CPI escalators baked into the original contract) as expansion overstates new selling motion. Expansion CAC Ratio and Net Revenue Retention are derived from this number.
Recurring revenue retained from the cohort of customers present at the start of the period, including expansion (upsell, cross-sell, price increases) and net of churn and contraction — but excluding revenue from net-new logos acquired in-period. Per the SaaS Metrics Standards Board (SMSB) NRR standard. NRR above 100% means the cohort grew faster than it lost — a hallmark of strong product-led expansion. The board reads NRR alongside GRR (`customers.gross_revenue_retention`) to separate the "keep + expand" signal from the "just keep" signal. Common pitfall: mixing GAAP revenue and ARR in numerator vs. denominator, or letting net-new logo revenue leak in — both inflate the number; SMSB is explicit that the cohort is closed at period start.
Contracted Annual Recurring Revenue — recognized MRR × 12 plus the annualized value of contracts that are signed but not yet live (i.e. implementation, ramp, deferred-start). Per the SMSB standard, CARR sits between ARR (live only) and pipeline (unsigned) on the revenue-certainty spectrum: contractually committed but not yet delivered. Boards reading CARR > ARR gap can quantify the in-flight implementation backlog and the leading indicator of next-period ARR. Common pitfall: counting verbal commitments or LOIs as CARR — only signed contracts qualify under the SMSB definition.
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