Retail Open-to-Buy Calculator

Understanding Open-to-Buy (OTB) Planning in Retail

Managing physical inventory is one of the most persistent challenges in retail and e-commerce. Purchase too much merchandise, and your capital becomes trapped in slow-moving stock, leading to storage issues and eventual markdowns. Purchase too little, and you run the risk of stockouts, frustrating customers and leaving potential revenue on the table.

An Open-to-Buy (OTB) plan is a financial budget specifically designed to manage inventory purchasing. It helps retail buyers and store owners determine exactly how much merchandise they can afford to bring in during a specific period without exceeding their inventory goals.

By looking at what you have, what you expect to sell, and where you want your stock levels to end up, an OTB calculation provides a clear, mathematical purchasing limit.

How the Calculation Works

At its core, Open-to-Buy is a balancing equation. It measures your total inventory needs against the inventory you already have or are waiting to receive. To use an OTB calculator effectively, you need to understand the variables involved.

Initial Markup (IMU %) Retail inventory is almost always planned at its retail selling value rather than its wholesale cost. However, when you write a purchase order to a vendor, you pay the cost price. The Initial Markup percentage is the bridge between these two numbers. If an item costs $50 and you sell it for $100, your IMU is 50%. The calculator uses this percentage to convert your retail OTB into the actual cash you have available to spend.

Beginning of Month (BOM) Inventory This is the total retail value of all stock available on the shop floor and in the backroom on the first day of the month.

Planned Sales This is the revenue you realistically expect to generate during the period. Accurate sales forecasting is essential here. If you overestimate your sales, the calculator will give you a larger purchasing budget, which can quickly lead to overstocking.

Planned Markdowns Markdowns include promotions, seasonal discounts, and inventory shrinkage (such as theft or damaged goods). When you mark an item down, you reduce the overall retail value of your inventory. Because your inventory value has dropped, you actually need to buy slightly more merchandise to replace that lost value and hit your end-of-month targets.

Target End of Month (EOM) Inventory This is the retail value of the stock you want to have left over on the last day of the month. You never want to end a month with zero inventory, as you need sufficient stock to support the next month's opening sales.

Goods On-Order This represents merchandise you have already ordered from suppliers that is scheduled to arrive during the current month. Since this stock is already on its way, it must be subtracted from your open purchasing budget.

The Math Behind the Budget

While the calculator handles the arithmetic, understanding the steps it takes helps clarify your purchasing strategy. The process happens in three phases.

First, it determines your Total Inventory Needs. This is the sum of your Planned Sales, Planned Markdowns, and your Target EOM Inventory. This number represents every item that will leave your store this month, plus the safety stock you want to keep on the shelves.

Next, it calculates your Total Available Stock. This is your Starting (BOM) Inventory plus any Goods On-Order.

Finally, it finds your Open-to-Buy limit. By subtracting your available stock from your total needs, you find your OTB at retail value. Applying your cost multiplier (based on your IMU) gives you the actual cash budget for writing purchase orders.

A Practical Example

Imagine a mid-sized clothing boutique preparing its purchasing budget for October. The buyer inputs the following data into their plan:

• BOM Inventory: $100,000
• Planned Sales: $50,000
• Planned Markdowns: $5,000
• Target EOM Inventory: $110,000
• Goods On-Order: $15,000
• Initial Markup: 50%

The store's total inventory needs for October are $165,000 (Sales + Markdowns + EOM). Their available stock is $115,000 (BOM + On-Order).

Subtracting the available stock from the total needs leaves an Open-to-Buy of $50,000 at retail value. Because the store operates on a 50% margin, the actual cash the buyer can spend with vendors is $25,000.

What Does "Overbought" Mean?

Sometimes, an OTB calculation results in a negative number. This condition is known in retail as being "overbought."

Being overbought means you currently have more inventory on hand—or scheduled to arrive—than your sales forecasts justify. If you have a negative OTB of -$10,000, your inventory is too heavy. In this scenario, purchasing should be immediately frozen. Buyers will typically need to negotiate with vendors to push back delivery dates on incoming orders, cancel unneeded purchase orders, or focus on aggressive sales strategies to clear out existing merchandise.

Common Mistakes in Inventory Planning

Failing to Account for Markdowns Many new retailers only look at sales and current inventory, completely forgetting to factor in discounts and shrinkage. If you plan to heavily discount merchandise for a holiday sale, your inventory value will deplete much faster than usual. Leaving markdowns out of the equation often results in under-buying, leaving the store looking empty by the end of the month.

Planning the Whole Store as One Category An overall store OTB is helpful for cash flow management, but it is a blunt instrument for actual purchasing. A healthy store might have a $0 total OTB, hiding the fact that the footwear department is completely sold out while the outerwear department is severely overstocked. OTB plans are most effective when calculated separately for distinct product categories or departments.

Optimistic Sales Projections A purchasing budget is only as reliable as the sales forecast it relies upon. If a buyer artificially inflates their planned sales to justify buying a new collection they like, they will inevitably end up with excess, aging stock. Forecasts should be based on historical data and realistic growth expectations.

Frequently Asked Questions

How often should I review my OTB plan? While planning is usually done on a monthly or seasonal basis, active buyers review their OTB weekly. As actual sales happen, the plan shifts. If the first week of the month brings in double the expected sales, your OTB for the rest of the month increases, allowing you to quickly reorder fast-selling items.

Does this concept apply to e-commerce? Yes. Whether you sell out of a brick-and-mortar storefront or a warehouse, the math of inventory movement remains identical. E-commerce businesses rely heavily on OTB planning to ensure they don't overspend capital on inventory that takes up expensive warehouse space.

What if I sell products with vastly different margins? If your store sells high-margin jewelry alongside low-margin accessories, calculating a single, store-wide IMU percentage will skew your cost budget. In these situations, it is highly recommended to run separate OTB calculations for each category using their specific average margins.

Should I spend my entire Open-to-Buy budget at the start of the month? Most experienced buyers hold back a portion of their OTB budget—often 10% to 20%—to react to unexpected trends. If a particular style suddenly goes viral or a vendor offers a surprise closeout deal, having unspent budget allows you to capitalize on those opportunities without overstocking your store.

Disclaimer: This tool and article are provided for educational and informational purposes only. Retail operations vary widely, and calculations are based on standard industry formulas. Always consult with a financial advisor, accountant, or professional inventory planner before making significant purchasing or budgeting decisions for your business.