Open-To-Buy Planning: A Guide to Inventory Control

Walk into any well-run store and you will notice something subtle: the shelves are full, but not overflowing, and the products people actually want are almost always available. That balance is rarely an accident. Behind it sits a disciplined system of inventory control, and at the centre of that system is a tool called the Open-To-Buy (OTB) plan. It is the financial guardrail that tells a buyer exactly how much new merchandise they can purchase in a given period without tying up cash in goods that will not sell. This guide breaks down how stock planning, the six-month merchandise plan, and the OTB calculation work together to keep a retail business healthy.

The critical role of inventory control 🔗

Inventory is usually the single largest investment a retailer makes. Get it right, and stock levels match demand smoothly. Get it wrong, and the business suffers in one of two ways. Carry too much, and capital sits frozen in unsold goods, storage costs climb, and items eventually have to be marked down. Carry too little, and customers walk away to a competitor when they find an empty shelf, costing both the sale and the relationship.

Good inventory control is about avoiding both extremes. An OTB plan helps a retailer stock the right quantity of the right products at the right time. As inventory planning specialists explain, OTB prevents over-buying while keeping cash flow steady, and it works best alongside other metrics such as sales forecasts and inventory turnover. In short, it turns purchasing from guesswork into a structured, data-led decision.

Store-level stock planning 🔗

Before any buying happens, a retailer needs to know what “the right stock” actually looks like at the store level. This is where stock planning begins, by breaking down broad merchandise into manageable pieces.

From categories to classifications 🔗

A retailer rarely plans inventory as one giant lump. Instead, broad merchandise categories are divided into classifications and then into sub-classifications. A clothing store, for example, might start with the category “menswear”, split it into classifications like shirts, trousers, and jackets, and then break shirts into formal shirts and casual shirts. This layered approach makes planning precise. It allows the retailer to see which narrow segment is selling and which is lagging, rather than relying on a vague sense of how the whole department is doing.

Building the unit stock plan 🔗

Once classifications are set, a unit stock plan is prepared. This plan details inventory not just in money terms but in actual units, broken down by price, style, colour, and size. The idea is to plan inventory the way a customer actually shops. A shopper does not want “a shirt”; they want a particular size, in a particular colour, at a price they are comfortable with. Planning at this level of detail ensures the assortment genuinely matches demand. This process of deciding how many items to carry and how many units of each is the heart of unit planning.

The model stock list and never-out items 🔗

Within unit planning, retailers use stock lists to keep inventory accurate. A model stock list describes the ideal assortment broken down by predictable factors such as classification, price, material, colour, and size. According to academic resources on apparel merchandising, the model stock plan is especially useful for fashion goods, which are identified by general characteristics rather than fixed specifications.

Closely linked is the idea of “never-out” items, the bread-and-butter products that customers always expect to find. A never-out list, as retail planning guides describe it, is a specially created list of key items or best sellers that get extra protection against the risk of running out. Think of staple goods like a standard white school shirt, a popular shade of hair oil, or a basic pair of black socks. These items rarely change, sell steadily, and damage customer trust the moment they disappear from the shelf. Guarding their availability is non-negotiable.

Developing a six-month merchandise plan 🔗

With store-level stock planning in place, the next layer is the merchandise plan, usually drawn up to cover a six-month period. The retail year is commonly split into two such periods, broadly aligning with major selling seasons. The plan acts as a tool that translates profit goals into a working framework for buying and control. It maps out, month by month, what should happen to sales, stock, and purchases.

Four key elements are planned for each month. Understanding them is essential because they feed directly into the OTB calculation.

Net sales estimates 🔗

Everything starts with a forecast of net sales, the projected revenue for each month of the plan. Buyers base these estimates on last year’s actual figures for the same season, current trends, and known events. In an Indian context, this means accounting for the surge around festivals such as Diwali, the wedding season, or back-to-school months, when demand for specific categories spikes sharply. Accurate sales estimates are the foundation; if they are wrong, every other number in the plan drifts off course.

Planned stock levels 🔗

Next come planned stock levels, the amount of inventory the retailer wants to have on hand. These are usually expressed as beginning-of-month (BOM) and end-of-month (EOM) stock, and they are linked in a chain: the EOM stock of one month becomes the BOM stock of the next. Stock levels are often set using a stock-to-sales ratio, which adjusts month to month depending on promotions, holidays, and seasonal demand. The goal is to hold enough inventory to support the sales target comfortably, with a sensible cushion, but no more.

Planned reductions 🔗

Not all inventory converts neatly into full-price sales. Reductions account for the unavoidable loss in inventory value from three main sources: markdowns (selling at sale prices), shrinkage (loss from theft, damage, or errors), and employee discounts. As merchandise budgeting guides note, reductions are typically calculated as a percentage of net sales and spread across the months, often weighted more heavily towards end-of-season clearance periods. Ignoring reductions is a classic planning error, because it makes a buyer believe more selling capacity exists than really does.

Planned purchases 🔗

Finally, the plan calculates planned purchases, the value of new merchandise needed to replenish what is sold and to maintain the desired stock level. This is where the four elements come together in a single formula:

Planned Purchases = Planned Sales + Planned EOM Stock + Planned Reductions − Planned BOM Stock

In plain terms, you add up everything you need to cover (sales, the stock you want left at the end, and reductions), then subtract the stock you already have at the start. The result is how much you genuinely need to bring in. This calculation can be done in retail value or at cost, and larger chains often work it out at both. The same logic applies at any time interval, monthly, weekly, or even daily, depending on how fast the retailer turns over stock.

Calculating your open-to-buy figure 🔗

Here is the crucial distinction many newcomers miss: planned purchases is not the same as how much you can still spend right now. A buyer almost always places some orders well in advance of the season. Those orders are commitments, money already promised to suppliers even if the goods have not yet arrived. The Open-To-Buy figure is what remains after accounting for them.

The calculation is straightforward:

Open-To-Buy = Planned Purchases − Commitments already placed

The OTB figure answers a single, practical question that inventory analysts call the heart of the system: how much more can I actually buy this month? It compares what you need against what you have already committed to, leaving you with your real, spendable purchasing power.

A worked example 🔗

Suppose a store plans purchases worth ₹8,00,000 of merchandise for a given month, based on its sales forecast, target stock, and expected reductions. The buyer has already placed advance orders worth ₹3,00,000 with suppliers. The Open-To-Buy for that month is:

₹8,00,000 − ₹3,00,000 = ₹5,00,000

That ₹5,00,000 is the amount the buyer is free to spend on new orders during the month without exceeding the plan. If they spend more, they risk overstocking and a cash crunch. If they spend far less, they may face empty shelves and lost sales.

Why smart buyers commit only half 🔗

A common and disciplined practice is to commit only about 50% of planned purchases upfront, leaving the remaining open-to-buy as flexible firepower. There are good reasons for this restraint. Holding back budget allows the buyer to reorder fast-moving items that sell better than expected, to respond to emerging trends mid-season, and to grab unexpected opportunities, such as a supplier offering an attractive deal on popular stock. A buyer who commits the entire budget early loses all of this agility and is locked into decisions made before the season even began. Maintaining an open-to-buy balance is, in effect, keeping options open. This flexibility is precisely why retailers with many SKUs, like apparel stores, lean so heavily on the system to stay organised and keep cash flow healthy.

Putting it all together 🔗

The three layers fit neatly. Store-level stock planning decides what the ideal assortment should be, down to size and colour. The six-month merchandise plan converts profit goals into monthly targets for sales, stock, reductions, and purchases. And the Open-To-Buy figure takes that plan and turns it into a live, working budget that controls spending in real time. Together they replace gut feeling with a structured method, ensuring products are on the shelf when customers want them, without locking away cash the business needs to stay nimble. For any retailer, mastering this discipline is one of the most direct routes to protecting both profit and customer loyalty.

What do you think? If you were running a clothing store during the festive season, how much of your buying budget would you commit upfront, and how much would you hold back as open-to-buy to chase fast-selling trends? And which products in your store would you place on a “never-out” list that must never be allowed to run out?

References

1. https://fitsmallbusiness.com/open-to-buy-planning/
2. https://www.mbaknol.com/retail-management/unit-planning-and-merchandise-lists/
3. https://vidyamitra.inflibnet.ac.in/data-server/eacharya-documents/56b0853a8ae36ca7bfe81449_INFIEP_79/53/ET/79-53-ET-V1-S1__unit_7.pdf
4. https://www.vskills.in/certification/tutorial/assortment-planning/
5. https://www.fibre2fashion.com/industry-article/9354/six-months-buy-plan-for-fashion-merchandising
6. https://www.faire.com/blog/buying/open-to-buy/
7. https://www.algo.com/blog/open-to-buy-planning/
8. https://www.shopify.com/blog/open-to-buy-plans