Buy Quantity Formula
How apparel buyers calculate the unit buy — with forecast, target EOP, BOP carry, and expected markdown baked in.
What Buy Quantity measures
Buy quantity is the number of units a buyer commits to a style given the sales forecast, target EOP position, starting BOP, and expected markdown drag.
Buy Units = (Sales Forecast Units + EOP Target − BOP) ÷ (1 − Expected Markdown %)Unlike OTB (which is in dollars at retail), buy quantity is the unit decision a buyer actually makes against a vendor PO.
Worked apparel example
A style: 3,000-unit sales forecast, 500-unit target EOP, 400 BOP carry, 12% expected markdown.
Buy Units = (3,000 + 500 − 400) ÷ (1 − 0.12) = 3,525 units
The markdown gross-up accounts for units that will be sold below full price but still consume inventory. Without it, the buy is chronically under-set and stock-outs land mid-season.
Buy 3,523 units. Cross-check against vendor MOQs and the size curve before issuing the PO.
Failure modes we see
Buy quantity = Sales forecast, period. No markdown gross-up, no BOP reconciliation, no EOP target. The buy consistently falls short in weeks 4–8; reorders arrive late; markdowns happen because the inventory was mis-timed.
How RetailNorthstar handles buy quantity
The buy quantity is derived live from the plan inputs — forecast, EOP target, BOP position, and expected markdown rate per style. Vendor MOQ rounding is applied and flagged. Chase capacity is held back against the remaining season.
Related formulas
- Receipt Plan — the dollar version of the buy
- Size Curve Allocation — how the unit buy distributes across sizes
- PO Coverage % — the coverage check
See buy quantity derived from plan — with MOQ rounding and size-curve split applied.
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