Buy Quantity Formula
How apparel buyers calculate the unit buy, with forecast, target closing stock, opening carry and expected markdown all built into the number.
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 ÷ (1 − markdown) gross-up assumes the sales forecast is full-price selling — markdown-driven units are incremental on top of it, consuming inventory the full-price forecast never counted. Without the gross-up, the buy is chronically under-set and stock-outs land mid-season.
Buy 3,523 units. The ÷(1 − markdown) gross-up assumes the sales forecast is full-price selling, with markdown units incremental. 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.
Book a Demo →