Open-to-Buy: How Retailers Calculate Inventory Budgets

Open-to-Buy

A retail planning method that helps determine how much inventory budget is available for future purchasing. It translates sales plans, markdowns, current inventory and desired inventory levels into a cash budget for buying, giving buyers and planners a numerical guide to weekly or monthly purchases.

Used by single-store owners and enterprise merchandising teams alike, an effective Open-to-Buy (OTB) program prevents overstocks, reduces out-of-stocks, and aligns cash flow with merchandise goals. This article explains the components of an OTB calculation, practical adjustments for modern omnichannel retailers, and the controls merchandisers use to keep inventory investment on plan.

What The Calculation Covers

At its simplest, OTB converts planned sales and desired ending inventory into a purchasing allowance. The standard components are beginning inventory, planned sales (for the period), planned markdowns, and desired ending inventory. From those figures you derive the amount of goods you can buy at retail and then convert to cost using a target margin or cost complement.

Why Open-to-Buy Matters

OTB connects merchandising strategy to working capital. Without it, buyers risk tying up cash in slow-moving items or missing sales opportunities due to insufficient stock. For a seasonal retailer, OTB provides a disciplined plan for ramping inventory into peak periods and clearing excess after seasonality.

Standard OTB Formula And Variations

The core formula many retailers use (in retail dollars) is:

Open-to-Buy = Planned Sales + Planned End-of-Period Inventory + Planned Markdowns - Beginning-of-Period Inventory

To convert to cost dollars for purchase orders, multiply the retail OTB by the cost complement (1 - target markup%). Retailers often adjust the formula for returns, transfers, or for including receipts already on order.

How It Varies By Business Model

OTB is not one-size-fits-all. Typical adjustments include:

• Omnichannel Allocation: Split planned sales by channel and maintain separate OTB ceilings for store and DC so replenishment meets channel demand.
• Seasonal Merchants: Apply week-by-week OTB during peaks (holiday, back-to-school) rather than monthly to preserve agility.
• High-Turn Discounters: Use shorter planning cycles (weekly) and smaller safety-stock assumptions because turns are fast and assortment shifts rapidly.

Who Is Responsible And Who Pays

Merchandising teams own OTB numbers; buyers and planners implement purchases against the plan. Finance often monitors compliance because OTB directly affects cash flow and working capital. In 3PL/omnichannel operations, warehouse managers and inventory controllers need visibility into OTB-derived receipts to plan space and labor.

Practical Example

Assume beginning inventory of $120,000, planned sales of $80,000, planned markdowns $5,000, and desired ending inventory $100,000. The retail OTB is $80,000 + $100,000 + $5,000 - $120,000 = $65,000. If the average cost complement is 60% (markup 40%), available purchase dollars at cost are $39,000 (0.60 x $65,000). Buyers use that figure to place purchase orders and manage receipts.

Common Pitfalls And Corrections

Several pitfalls reduce OTB accuracy:

• Inaccurate Inventory Data: Miscounted stock or slow cycle counts distort beginning inventory and break the plan.
• Ignoring Lead Times: Long or variable supplier lead times require earlier purchase decisions and safety stock buffers.
• Static Assortments: Treating OTB as a fixed monthly number during a season of rapid trend change leads to missed opportunities or markdown risk.

Tools And Automation

Modern WMS, ERP, and dedicated planning modules automate OTB calculations and connect them to purchase orders, open PO tracking, and receipts. Integration with POS and e-commerce sales data lets buyers refresh OTB weekly or even daily. The automation also surfaces exceptions: slow-turn SKUs, unexpected sell-through, and PO variances.

Tips For Implementation

• Start Simple: Use a monthly OTB for your first year, then shorten granularity as data confidence grows.
• Reconcile Often: Reconcile actual receipts and vendor invoices to the OTB plan weekly to avoid drift.
• Use Scenario Planning: Run conservative and aggressive OTB scenarios for promotional periods so you're prepared to shift spend.

In short, the Open-to-Buy A retail planning method that helps determine how much inventory budget is available for future purchasing. When calculated accurately and used with disciplined purchasing controls, OTB keeps inventory investment aligned with sales goals and cash flow needs.