Buy Planning

What is buy planning?

Buy planning is the apparel merchandising process of converting assortment decisions into structured purchase commitments. A buy plan specifies how many units of each style, color, and size to purchase — from which vendors, at what cost, and for which selling channels.

Buy planning sits between assortment planning (which establishes what to carry) and purchase order generation (which formalizes the commitment with the vendor). It is the step where strategy becomes binding inventory commitment.

A complete buy plan captures six dimensions for each purchase decision:

1. →Style — the specific product being purchased
2. →Color — colorway within the style
3. →Size — units by size, derived from the size curve
4. →Channel — DTC, wholesale, store split for this style
5. →Vendor — factory or supplier fulfilling the order
6. →Cost — unit cost and landed cost per vendor

How buy planning connects to OTB

A buy plan that exceeds OTB is not a valid plan — it represents a financial commitment the brand cannot support within its planned inventory budget. Buy planning must therefore operate against a live OTB position, not a static budget figure.

In practice, buyers update quantities, add styles, or shift vendor splits throughout the buy planning process. Each change affects the total cost commitment and therefore the OTB position. When these two processes are disconnected — OTB in one spreadsheet, buy plan in another — the reconciliation step is manual and often deferred until the night before the buy review.

In a connected system, OTB and the buy plan share a data model so cost commitments update the OTB position in real time. Buyers see their remaining budget at every point in the process without switching files or running manual calculations.

Buy planning vs assortment planning

These terms are sometimes used interchangeably but describe distinct steps:

Assortment planning determines what to carry: which styles, colors, and depths belong in the season's product mix.

Buy planning determines how to purchase it: which vendor supplies each style, at what quantity per size, across which channels, and at what landed cost.

The buy plan is generated from the assortment plan. In a manual workflow, this handoff requires re-entering assortment data into a separate buy planning spreadsheet — introducing errors and creating two sources of truth. In a connected system, assortment decisions flow directly into the buy plan without re-entry.

Size curves in buy planning

One of the most labor-intensive aspects of spreadsheet buy planning is size quantity entry. For each style in the assortment, a buyer must specify how many units to buy in each size. On a 150-style buy, this means entering size quantities hundreds of times — each entry a potential error.

A buy planning tool with stored size curves applies the correct ratio to each style automatically. Size curves are defined by category, channel, and demographic segment — and can be overridden at the style level when historical data or product type warrants a different distribution.

Vendor management in buy planning

Buy plans often involve multiple vendors. A single style may be sourced from different factories across colorways. Vendor minimums — the minimum order quantity required by a factory to fulfill an order — affect how deeply a style can be purchased and whether certain colorways are economically viable.

A complete buy plan tracks vendor assignment per style-color combination, the applicable minimum order quantities, and the cost implication of buying at minimum vs above minimum. Styles that cannot be sourced at viable minimum order quantities may need to be cut from the assortment at the buy planning stage, requiring a reconciliation back to the assortment plan.