OTB vs WSSI: what’s the difference?
Open-to-buy (OTB) is a budget control that tells you how much more stock you can receive without exceeding plan, while a WSSI (Weekly Sales, Stock & Intake) is a weekly trading view that tracks the flow of stock through a season — closing stock = opening stock + intake − sales. OTB is the budget; the WSSI is the working plan the budget lives inside, and most apparel teams use both.
They are two views of the same plan — one answers “how much can I buy,” the other shows “how stock will flow week by week.”
- Definition — Open-to-buy (OTB)
- Open-to-buy is the amount of inventory a team can still receive in a period — in cost, retail value, or units — without exceeding its inventory plan. It is the buying guardrail that sits at the point of purchase, derived from planned sales, planned closing stock, planned markdowns, and stock already on hand or on order.
- OTB = planned sales + planned closing stock + planned markdowns − opening stock − on-order
- Used by: Buyers and planners committing spend against a financial plan
- Related: WSSI, buy plan, weeks of supply, sell-through
Open-to-buy
Open-to-buy is the amount of stock you can still commit to receive in a period without breaking your inventory plan. It is calculated from planned sales, planned closing stock, planned markdowns, and stock already on hand or on order. The output is a budget — usually in cost or retail value, sometimes in units — that keeps buying inside the financial plan. See the open-to-buy calculator for the working math.
WSSI
A WSSI projects sales, stock, and intake for every week of a season. Each week’s closing stock becomes the next week’s opening stock, so you can read across the weeks and see where you will run short or pile up — early enough to adjust intake or markdowns. It is the standard in-season trading tool for merchandisers. The what is a WSSI guide walks through the three lines and the formula in detail, and the WSSI calculator projects closing stock and weeks of cover.
OTB vs WSSI, side by side
| OTB | WSSI | |
|---|---|---|
| Primary purpose | Control the buying budget | Track weekly stock flow and trade in-season |
| Time horizon | A buying period (month, quarter, season) | Week by week across the season |
| Main users | Buyers and planners committing spend | Merchandisers trading in-season |
| Key inputs | Planned sales, planned closing stock, markdowns, on-hand and on-order stock | Weekly sales, opening stock, planned intake |
| Key outputs | Remaining budget to buy (value or units) | Closing stock and weeks of cover per week |
| Best for | Setting and protecting the buy budget | Managing intake, cover, and markdown timing |
| Common spreadsheet issue | Lives in a separate workbook from the WSSI, so the two drift apart | Hard to maintain weekly across many lines and channels |
- OTB
- Control the buying budget
- WSSI
- Track weekly stock flow and trade in-season
- OTB
- A buying period (month, quarter, season)
- WSSI
- Week by week across the season
- OTB
- Buyers and planners committing spend
- WSSI
- Merchandisers trading in-season
- OTB
- Planned sales, planned closing stock, markdowns, on-hand and on-order stock
- WSSI
- Weekly sales, opening stock, planned intake
- OTB
- Remaining budget to buy (value or units)
- WSSI
- Closing stock and weeks of cover per week
- OTB
- Setting and protecting the buy budget
- WSSI
- Managing intake, cover, and markdown timing
- OTB
- Lives in a separate workbook from the WSSI, so the two drift apart
- WSSI
- Hard to maintain weekly across many lines and channels
When to reach for open-to-buy
Use OTB when you are deciding how much to commit. Before placing orders, OTB tells you how much budget is left against the plan so you do not over-buy into a category or period. It is the control that sits at the point of purchase, and it is the number buyers check before signing off a buy.
When to reach for the WSSI
Use the WSSI when you are trading in-season. It is the view you read weekly to see how stock is flowing, where cover is thin or heavy, and when to pull intake forward, push it back, or take markdown. It turns the budget set by OTB into a live, week-by-week picture of the stock position.
Why UK and European teams often rely heavily on WSSI
In UK and European apparel and retail, the WSSI is the everyday language of in-season trading. Merchandisers run weekly WSSI reviews to manage intake, cover, and markdown, with open-to-buy used as the buying guardrail around it. In some other markets the headline term is open-to-buy, but the underlying flow — sales, stock, intake — is the same. The retail math formulas guide collects the calculations behind both views.
Why both break when managed manually
OTB and the WSSI describe the same plan from two angles, but in spreadsheets they usually live in separate files. A change to planned intake on the WSSI should move the OTB, and a buy committed against OTB should appear on the WSSI’s intake line — but with separate workbooks, that only happens when someone re-keys it. Across many lines, colours, and channels, the two drift apart and decisions get made on stale numbers.
How connected planning helps
From line plan to production, RetailNorthstar connects merchandising, design, buying, sourcing, and operations in one workflow. OTB and the WSSI become two views of the same live plan — commit a buy and the WSSI’s intake line and the OTB budget both update, so trading decisions are made on one consistent set of numbers.
Frequently asked questions
- What is the difference between OTB and WSSI?
- Open-to-buy (OTB) is a budget control that answers “how much more stock can I receive without exceeding plan.” A WSSI (Weekly Sales, Stock & Intake) is a weekly trading view that tracks the flow of stock through a season: closing stock = opening stock + intake − sales. OTB is a budget; the WSSI is the working plan that the budget sits inside.
- Do I need both OTB and WSSI?
- Most apparel planning teams use both. OTB sets the buying guardrail; the WSSI shows the weekly flow of sales, stock, and intake so you can trade against that guardrail. The WSSI’s intake line and the OTB number are directly related — the WSSI shows the flow, OTB shows the remaining budget to buy.
- Why do UK and European teams rely so heavily on the WSSI?
- In UK and European apparel and retail, the WSSI is the standard in-season trading tool. Merchandisers manage intake, cover, and markdown decisions week by week off the WSSI, with OTB used as the buying control around it. In some other markets, open-to-buy is the more familiar headline term.
- Can a spreadsheet handle both OTB and WSSI?
- A spreadsheet can model both, but they tend to drift apart once you run them weekly across many lines and channels. The OTB workbook and the WSSI workbook are usually separate files, so a change in one is not reflected in the other until someone re-keys it — which is where errors and stale numbers creep in.
- OTB controls financial buying capacity — how much inventory you can still commit within plan.
- A WSSI manages inventory flow over time, tracking weekly sales, stock, intake, and cover.
- Apparel brands often need both: OTB for the buying guardrail, the WSSI for in-season trading.
- Spreadsheets work early but get harder to keep in sync as teams, channels, and receipts change.
- RetailNorthstar connects OTB, WSSI, assortment, buy plans, POs, and production in one live plan.
See how RetailNorthstar connects OTB, WSSI, intake, assortment, and buy plans.