Open-to-Buy Planning: How Much Stock Can You Afford to Buy?

Open to buy is the amount of new stock, at cost, you can still receive in a month after allowing for what you expect to sell, the stock you want left at month end, and what you have already ordered. The formula is: planned cost of sales + planned write-offs + planned closing stock − opening stock − stock already on order.

That one line is the easy part. The hard part is choosing sensible inputs, running the formula month by month so each month’s closing stock becomes the next month’s opening stock, and turning the result into purchase orders you can actually pay for.

On this page you get a fully worked six-month example with every figure checked, a downloadable Excel template that does the arithmetic for you, a step-by-step method, decision rules for when the number goes negative, and how to pull the inputs from Cash Flow Inventory.

What open to buy means, and what it is not

Open to buy is a purchasing budget expressed as stock. It answers one question for each month: how much new merchandise can arrive without pushing your stock above the level you planned? It comes from retail buying, but it works just as well for a wholesaler, an online seller or a pharmacy.

It is not a sales forecast, although it starts with one. It is not a reorder point either. A reorder point tells you when a single item needs topping up. OTB sets the money ceiling across a category or the whole business, and your item-level reorders have to fit under it. If you already use min and max stock levels, think of OTB as the check that the sum of all those reorders still makes financial sense.

It is also different from a general business budget. Your small business budget plans revenue and expenses. OTB plans the stock you carry between them, which is where most product businesses tie up most of their cash.

The open-to-buy formula, part by part

Open to buy = planned cost of sales + planned write-offs + planned closing stock − opening stock − on order

Every term is at cost, including freight and duty where you capitalise them. Mixing retail and cost values in one line is the most common reason an OTB number makes no sense.

• Planned cost of sales: planned sales revenue × (1 − gross margin). If you plan sales of 40,000 at a 45% margin, cost of sales is 40,000 × 0.55 = 22,000. The gross margin calculator helps if you only know markup.
• Planned write-offs: stock that leaves without being sold. That includes shrinkage, damage, expiry, samples and items given away. It is small but real, so leave it out and you will run short.
• Planned closing stock: the stock you want on hand at month end. A practical rule is cover: closing stock = next month’s planned cost of sales × target months of cover.
• Opening stock: for the first month, your actual stock at cost today. For later months, the previous month’s planned closing stock.
• On order: purchase orders already placed that are due to arrive in that month, at landed cost. This is money already committed.

The logic is simple. The first three terms are the stock you need to have passed through or be holding. The last two are the stock you already have or have already bought. The gap is what you are still free to buy.

Worked example: a six-month open-to-buy plan

What the example tells the owner

January is tight. Only 6,100 is open because she starts the year with 34,000 of stock and 12,000 still arriving. Any January buying should go to proven sellers, not new lines.

April carries the biggest budget, at 32,850, because it has to build stock for May’s peak. May’s closing stock then falls to 39,600 because June and July are quieter. Planned stock drops on purpose ahead of a slower season, and the OTB figure shrinks to match.

How to build your open-to-buy plan, step by step

1. Choose the level. Plan the whole business first, then split by category once you trust the numbers. Category plans stop a strong category from hiding a dead one.
2. Forecast sales by month at retail. Start from the same months last year, adjust for known changes such as a new channel, a price rise or a lost customer, and be honest about seasonality.
3. Convert to cost. Multiply by (1 − planned gross margin). Use a lower margin in clearance months.
4. Estimate write-offs. Use your adjustment history from stock counts. If you have none, start with a small round figure and refine it after each count.
5. Set planned closing stock. Pick a months-of-cover target for each category and multiply it by next month’s cost of sales. Fast movers need less cover than slow, high-margin lines.
6. Enter actual opening stock for the first month at cost, then chain: each opening equals the prior planned closing.
7. List open purchase orders by arrival month at landed cost.
8. Calculate OTB and read the result. A positive figure is your ceiling. A negative figure is a warning.
9. Update monthly. Replace the next month’s opening stock with the actual figure, refresh on-order, and reforecast sales if you are off plan.

The spreadsheet columns and formulas

The download has two sheets. You can also build it yourself in a few minutes.

Turning open to buy into orders and cash

OTB is budgeted by the month goods arrive. That creates two timing shifts you have to manage.

Order timing. Subtract the supplier’s lead time. If an importer quotes eight weeks, April’s 32,850 has to be placed by early February. Write the “order by” date next to each month so nobody discovers April’s budget in April.

Payment timing. Then apply payment terms. On 30-day terms, April’s receipts are paid in May, the month sales peak at 56,000, so the cash should be there. If that supplier wants payment in advance, you pay in February, when planned sales are only 36,000. Same OTB, very different strain on the bank. This is the same lever covered in our cash conversion cycle worked example.

Common open-to-buy mistakes

• Mixing retail and cost. If sales are at retail and stock is at cost, OTB is overstated by your whole margin. Convert first.
• Using a stale opening stock. One wrong opening figure flows through every later month. Take it from your books after a recent stock count.
• Forgetting on-order. Orders placed weeks ago are easy to miss, and buying again on top of them is how overstock happens.
• Counting dead stock as available cover. Stock that will not sell still sits in opening stock and shrinks your OTB without supporting sales. Separate it using FSN analysis and plan its clearance as a write-off or markdown.
• Planning once a year. OTB is a rolling plan. A January plan that is never updated is a guess by March.
• Treating OTB as a target. It is a ceiling. Leaving budget unspent because sales are soft is the plan working, not failing.

Edge cases generic answers skip

When open to buy is negative

A negative number means planned stock at month end would exceed your target even if you bought nothing. Work through it in this order: delay the arrival of open orders, reduce quantities, cancel what you can on fair terms, then plan clearance. Do not carry the deficit forward silently, because it hides inside next month’s opening stock.

Markdowns when you plan at cost

A markdown does not change what the stock cost you. It lowers revenue. In a clearance month, keep cost of sales at the cost of the units you expect to sell, and lower the planned margin so revenue and cash-in reflect the discount.

Imports, minimum order quantities and landed cost

Include freight, duty and clearing in on-order and in your stock values, consistent with how you value inventory under your accounting rules. IAS 2 Inventories includes costs of purchase such as import duties and transport in inventory cost. If a supplier’s minimum order quantity exceeds one month’s OTB, spread it across the months it will sell through and check the cover it creates.

New products and launches

New lines have no history, so give them a separate, capped OTB line rather than mixing them into a category with a track record. Review sell-through after the first few weeks before releasing more.

Several locations or channels

Plan OTB per location if stock cannot easily move between them. If stock is shared across your store and marketplaces, plan one pool, and set the closing stock high enough to cover every channel’s demand. That links naturally to a monthly sales and operations planning review.

How to do this in Cash Flow Inventory

Cash Flow Inventory does not have a dedicated open-to-buy screen. Keep the calculation in the template and use the app for the inputs and the controls around it.

1. Find your on-order figure. In Settings › Purchase, set Purchase process to Order → receive → bill → payment, so orders and goods receipts are recorded. Then open Purchasing › Purchase orders and use the To receive view, which lists approved orders whose goods are still to come. Group them by expected arrival month into the Open orders sheet. Under What purchase documents carry, show Cost lines and Landed cost, so freight and duty sit on the order and your on-order figure is at landed cost.
2. Build the sales side of the plan. Open Accounting › Budget by account, choose the Fiscal year (Calendar year or July – June), the Year and the Budget scenario, then use Fill from last year… to start from last year’s actuals. Adjust the monthly revenue and cost of sales amounts to match your OTB plan and save. Budgets cover revenue and expense accounts only. Stock is a balance-sheet figure, so closing stock stays in the spreadsheet.
3. Check cash timing. Open Budget forecast to see the plan as money in and out by month, which is where you test whether your receipts can be paid for when they fall due.
4. Track and reforecast. Switch Budget by account to Actual or Variance, or run the Budget vs actual report. Actuals are read live from the books. If sales drift, choose the Reforecast scenario, copy the Budget into it, change the months ahead, and update your OTB sheet to match. Best case and Worst case scenarios let you see the OTB you would have under each.
5. Put a guardrail on spending. Set Purchase order approval to Approve automatically up to an amount, so larger orders wait in Waiting for approval while someone checks them against the month’s OTB. If you publish a purchase order workflow in Settings › Workflows, its steps decide instead.
6. Act on a negative OTB. Cut quantities on open orders, or use Cancel order and choose a reason such as No longer needed. Close order records why an order finished short, for example Cancelled the rest.

The full procedures are in the purchase orders guide and the budgeting and forecasting guide.

Frequently asked questions

What is the open to buy formula?

Open to buy = planned cost of sales + planned write-offs + planned closing stock − opening stock − on order. Calculate it for each month, at cost, and carry each month’s planned closing stock forward as the next month’s opening stock.

Should open to buy be calculated at cost or at retail?

Either works if you are consistent, but cost is more useful for small businesses because the result is the money you will actually spend. Retail OTB is common in large department stores that run the retail inventory method. Never mix the two in one formula.

How often should I update my open-to-buy plan?

Monthly at a minimum. Each month, replace the next month’s opening stock with your actual stock value, refresh open orders, and reforecast sales if you are running off plan. Fast-moving seasonal businesses often check it weekly during peak buying.

How do I set planned closing stock?

Multiply next month’s planned cost of sales by a target months of cover, for example 1.5. Base the cover on supplier lead time and how reliable demand is. Your stock turn is a good sense check, and the inventory turnover calculator shows what your current cover implies.

What does a negative open to buy mean?

It means you are overbought for that month. Even with no new orders, stock would end above plan. Delay or reduce open orders and plan clearance before buying more.

Is open to buy only for retailers?

No. Wholesalers, online sellers and pharmacies use the same logic, and manufacturers can apply it to purchased materials. Any business that buys stock ahead of selling it benefits from a monthly ceiling on receipts. The U.S. Small Business Administration’s finance guide covers the wider cash-planning habits it fits into.

Open to buy works best when the inputs are live: real stock values, real open orders and actuals you do not have to type in. If you want purchase orders, approvals and budget against actual in one place alongside your template, start a free trial of Cash Flow Inventory and build your first six-month plan from your own numbers.