Open-to-Buy Planning:
Formula, Example & Template
Open-to-buy (OTB) is the retail budgeting method that stops you over-committing cash to stock. The formula, a worked monthly example, a template table you can copy, and how Replenagise automates the whole plan.
By Replenagise · Updated 11 July 2026 · 6 min read
What is open-to-buy — and the formula
Open-to-buy is the amount of inventory budget you still have available to spend for a period without over-stocking. The core formula:
OTB = Planned Sales + Planned End-of-Month Stock − Opening Stock − Stock on Order
In words: work out what you expect to sell, add what you want left on the shelf at the end of the month, subtract what you already hold and what is already on its way. What remains is what you are genuinely open to buy. Run it monthly per category (or per supplier) and your purchasing budget tracks demand instead of habit.
A worked monthly example
1. Plan the month’s sales
Your forecast says the Apparel category should sell £40,000 at retail value in March, based on last year’s March adjusted for this year’s trend.
2. Set the closing stock target
To keep availability healthy into April you want £30,000 of stock left at the end of March — roughly three weeks of cover at the forecast run rate.
3. Count what you already have
Opening stock on 1 March is £35,000, and £10,000 of purchase orders are already placed and due in during the month.
4. The OTB result
OTB = 40,000 + 30,000 − 35,000 − 10,000 = £25,000. That is the budget still available for March buys. A negative result means you are already over-bought — stop purchasing and clear stock instead.
From monthly OTB table to automated plan
A classic OTB template is a monthly table per category with rows for planned sales, planned closing stock, opening stock, on-order, and the resulting open-to-buy. It works — and it also goes stale the moment sales deviate from plan, which is why OTB spreadsheets get rebuilt every month-end by whoever drew the short straw.
Replenagise runs the same discipline continuously. Its OTB planning uses live sales, live stock, and live on-order quantities from Shopify and Linnworks, forecasts the demand side per SKU, and recalculates what you are open to buy as the month actually unfolds. The budget conversation moves from “what did the spreadsheet say last Tuesday” to “what does demand say right now”.
Related reading: choose the sales plan with demand forecasting methods, size individual orders with the EOQ formula, and see how inventory forecasting software and purchase order software execute the plan.
Open-to-Buy — FAQs
What is open-to-buy in retail?
Open-to-buy is a purchasing budget method: the amount you can still commit to inventory for a period without ending up overstocked. It is calculated as planned sales plus planned closing stock, minus opening stock and stock already on order.
How do you calculate open-to-buy?
OTB = Planned Sales + Planned End-of-Period Stock − Opening Stock − On-Order. Using retail values keeps it comparable with sales plans; some teams run it at cost instead — either works if you are consistent.
What does a negative open-to-buy mean?
You are already committed beyond the plan: current stock plus incoming orders exceed what the period needs. The response is to pause discretionary buying, chase sell-through (promotions, channel shifts), and let the position unwind before placing new POs.
Can open-to-buy be automated?
Yes. Replenagise includes OTB planning driven by live data: demand forecasts set the sales plan, stock and on-order sync from Shopify and Linnworks, and the open-to-buy position updates continuously instead of at month-end. Purchase orders raised in the platform respect the budget you set.
Run OTB on Live Data, Not Last Month’s Spreadsheet
Forecast-driven open-to-buy planning with live stock and on-order positions — connected straight to Shopify and Linnworks.