The commission formula (with accelerators)
up to quota: sales × base rate
above quota: (sales − quota) × accelerator rate
total pay = base salary + both commission pieces
Accelerators exist because the last dollars of the month are the hardest to close — plans reward them at a higher rate. If your plan has tiers instead (different rates at 80%, 100%, 120% of quota), run each tier's slice separately with the same logic.
A worked example
$4,000 base, $50,000 in sales against a $40,000 quota, 5% base rate with an 8% accelerator: the first $40,000 pays $2,000, the $10,000 above quota pays $800, so the month totals $6,800 — an annualized pace of $81,600. Notice the accelerator made the over-quota sales worth 60% more per dollar; that's the incentive doing its job.
Reading a comp plan before you sign
Three questions catch most surprises: Is commission paid on booking or on cash collected? Is there a cap (a ceiling on commission no matter how much you sell)? And is any of the base a "draw" — an advance against future commission that you effectively pay back? Each of these changes what an identical headline rate is really worth.
Why the commission check is smaller than the math above
Commissions are supplemental wages, so when paid separately from base salary they're typically withheld at a flat 22% federal rate plus Social Security and Medicare (7.65%) and state tax. On a $2,800 commission in a 5% state, expect roughly $975 withheld — about $1,825 in the check. Withholding isn't your final tax: it reconciles when you file, just like a bonus — the bonus tax calculator breaks down that same supplemental-wage withholding in detail.