What is Sales Capacity Model?
A sales capacity model forecasts revenue by calculating the productive selling capacity of each rep based on ramp time, quota, historical attainment, and attrition, giving CROs a bottoms-up revenue prediction.
A sales capacity model is the quantitative foundation for revenue planning. Instead of setting a revenue target and dividing by quota (top-down), it builds the forecast from the ground up: how many reps you have, how ramped they are, what they can realistically produce, and how attrition affects output. Every CRO should build one before committing to a number.
How to Build a Capacity Model
Start with your current headcount by role (AE, SDR, AM). For each rep, assign a ramp status: fully ramped, partial ramp (0-3 months = 25% productivity, 3-6 months = 50%, 6-9 months = 75%, 9+ months = 100%). Multiply each rep's quota by their ramp factor and their historical attainment rate. Sum across all reps for total expected production. Then subtract expected attrition: if annual turnover is 25%, you'll lose a quarter of your team over the year, and backfills take 3-6 months to ramp. The gap between capacity model output and the board's target is your hiring plan.
Capacity Model Variables
The key inputs: number of quota-carrying reps, individual quota targets, average ramp time to full productivity, ramp productivity curve (what percentage of quota a new hire produces at each stage), historical attainment rate for ramped reps, expected attrition rate, time to backfill open roles, and new hire start dates. Each variable has a meaningful impact. Changing ramp time from 6 months to 9 months can reduce annual capacity by 10-15% if you have a lot of new hires.
Why Boards Want This
Boards want to see a capacity model because it translates a revenue target into specific operational requirements: headcount, hiring timeline, ramp investment, and risk factors. A CRO who says 'we need 10 more AEs to hit $50M' without a capacity model is guessing. A CRO who shows the model connecting headcount, ramp, attainment, and attrition to a revenue number is building confidence. Capacity models also reveal whether a target is achievable with the current plan or requires changes to hiring pace, quota, or go-to-market strategy.
Common Mistakes
Using 100% attainment as the assumption for ramped reps. Historical average attainment is typically 55-65%. Building a model that assumes every rep hits quota will over-project revenue by 35-45%. Another mistake: ignoring attrition. If you plan for 20 ramped AEs but don't account for 5 leaving mid-year, your actual producing headcount drops to 15 plus some ramping backfills. The model should include a monthly attrition assumption and the lag time to rehire and ramp replacements.
In Practice
Build the model in a spreadsheet with monthly columns across 12 months. Row by row, list each current rep and planned hire with their start date, ramp stage, quota, and expected attainment. Sum each month to get a monthly capacity forecast. Compare this to the monthly revenue target. The delta tells you exactly when you're under-capacity and how many hires you need. Update the model monthly with actual starts, departures, and attainment data. The gap between model and actuals is your forecast risk, and it should shrink over time as your assumptions get more accurate.
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