How to Stress-Test Your Apparel Buy Before You Place the PO
Insights from Mary Wiegand, Founder & CEO of Boon — a demand planning and inventory management consultancy specializing in fashion and apparel brands.
There's one question that changes how founders think about a seasonal buy more than any other.
Not "what do you expect to sell?" Not "what did you sell last season?" Not "what's your revenue target for the year?"
This one: what happens if your sell-through assumption is wrong by 20 points?
Most founders have never answered it. They've picked a number — usually an optimistic one — and built everything around it. The buy quantity, the production budget, the cash flow projection for the season. All of it anchored to a sell-through assumption that's never been explicitly stress-tested.
When you actually sit down and model what 60% sell-through means instead of 80% — what it does to your cash position, your margin, your ability to fund next season — the number you were comfortable with starts to feel a lot less comfortable.
That discomfort is the point.
The Locked Bet Problem
Most planning content assumes you have flexibility during the season. You can chase what's working. You can pull back on what isn't. You can shift open-to-buy dollars toward the styles and sizes that are outperforming, and reduce exposure on the ones that are lagging.
Many apparel brands don't have that flexibility. One seasonal buy. One PO. Whatever ships is what you have for the entire selling period.
When you're operating with a single buy and no replenishment, every unit is a locked bet placed months before the consumer weighs in. The decisions that determine your season's outcome — how much to buy, in which styles, in which sizes, at what price — are made long before you have any market signal to validate them.
In this structure, the only real lever you have is the quality of the decision before the PO goes out. There's no fixing it mid-season. There's no responding to data that doesn't exist yet. The stress-test isn't a risk management exercise. It's the last checkpoint before you commit to a position you'll live with for the next six to twelve months.
What the Stress-Test Actually Is
A buy stress-test is a simple scenario model. You take your planned buy and run it through multiple sell-through outcomes to understand what each one means in concrete terms.
Start with three scenarios:
Base case: Your expected sell-through. The number you've been planning against. What does the season look like if everything goes roughly to plan?
Downside case: Your expected sell-through minus 15–20 percentage points. Not a catastrophe — just a miss. What does the season look like if the product performs meaningfully below your expectation?
Stress case: Your expected sell-through minus 30–35 percentage points. A genuinely bad season. What does this do to the business?
For each scenario, calculate the specific outcomes:
Ending inventory: How many units are left at end of season? What is the dollar value of that inventory at cost?
Markdown depth required to clear it: If you need to move the remaining units, at what discount do they clear, and what does that do to your realized margin?
Cash impact: What's the total cash that went out to fund this buy, and how much comes back after markdowns? What's the gap?
Effect on next season: After this season closes, how much cash is available to fund the following buy? Does a downside scenario leave you with enough to maintain the same business, or does it require you to buy smaller, defer payments, or make other accommodations?
This last question is the one that matters most and gets skipped most often. Founders think about the current season's inventory problem. They don't always think about how that inventory problem cascades into the next season's buying power.
Running the Numbers
Here's a simplified version of how the model works.
A brand is planning a seasonal buy of 2,000 units at an average wholesale cost of $28 per unit. Total buy cost: $56,000. Average planned retail price: $85 per unit.
They're planning for 80% sell-through at full price, with the remaining 20% selling at 40% off.
Base case (80% full price, 20% at 40% off):
- 1,600 units × $85 = $136,000
- 400 units × $51 = $20,400
- Total revenue: $156,400
- Gross margin after cost: $100,400
Downside case (60% full price, 40% at 40% off):
- 1,200 units × $85 = $102,000
- 800 units × $51 = $40,800
- Total revenue: $142,800
- Gross margin after cost: $86,800
- Delta from base case: −$13,600
Stress case (45% full price, 35% at 40% off, 20% unsold/donated/destroyed):
- 900 units × $85 = $76,500
- 700 units × $51 = $35,700
- 400 units × $0 = $0
- Total revenue: $112,200
- Gross margin after cost: $56,200
- Delta from base case: −$44,200
These numbers are illustrative, not precise — your actual unit economics, markdown strategy, and channel mix will produce different figures. The point isn't the exact output. It's that you've run the calculation before committing, so the decision is made with eyes open.
For a brand doing a $56,000 buy, the difference between a base case and a stress case outcome is $44,000 in gross margin. For most founder-led brands, that's not an abstract number — it's a significant portion of the season's operating cash.
The Question That Unlocks the Conversation
The most common reason founders don't run this analysis is that nobody has ever explicitly asked them to. They're moving fast, the buy feels right, and modeling a downside scenario feels like inviting pessimism into a process that's running on momentum.
But the question isn't pessimistic. It's protective.
What did your last bad buy actually cost you? Not the inventory value — the cash that went out and didn't come back. The wholesale cost of the units that got marked to 40% off. The storage fees accumulating on what didn't sell. The effect on your ability to fund the following season.
Nine times out of ten, when a founder actually calculates that number, it's larger than they realized. And once it's real — once it has a dollar amount attached to it — the conversation shifts. It stops being "can I afford planning support?" and starts being "can I afford another season without it?"
The stress-test creates the same shift before the buy, not after. It makes the risk concrete enough to inform the decision, rather than abstract enough to ignore.
What to Do With the Output
The goal of the stress-test isn't to talk yourself out of the buy. It's to make a better version of it.
A few things the scenario model often surfaces:
The buy quantity needs to come down. When the downside scenario produces a cash outcome the business can't absorb, the response isn't to accept the risk — it's to reduce the bet. A smaller buy with the same sell-through assumptions produces better margin at every scenario level, at the cost of leaving some upside on the table.
The size or style mix needs to shift. Sometimes the aggregate buy is defensible but the allocation within it isn't. Stress-testing by style or by size category often reveals that the risk is concentrated in specific parts of the buy — the fashion styles, the new colorways, the unproven silhouettes — rather than spread evenly. Reducing depth on the speculative pieces while holding depth on core styles improves the downside scenario without shrinking the overall buy proportionally.
The markdown plan needs to be built in advance. If the downside scenario requires aggressive clearance activity to recover cash, that clearance strategy should be defined before the season starts, not improvised after. What channel will you use? What discount depth triggers action? At what point in the season do you start? Having answers to these questions in advance means the response to a bad sell-through week is a plan execution, not a crisis.
The next season's buy needs a cash reserve. If the stress case leaves you with insufficient cash to fund a full buy next season, that constraint needs to be visible now — while you can build a reserve into this season's financial plan — rather than discovered after the season closes.
The Habit That Prevents the Problem
The brands that consistently avoid catastrophic inventory outcomes aren't necessarily better at predicting what will sell. They're better at slowing down the decision long enough to ask the right questions before money moves.
Building a stress-test into the pre-buy process isn't complicated. It's a spreadsheet, a few scenarios, and a conversation about what each one means for the business. It takes a few hours before a PO goes out.
The alternative: discovering the downside scenario in real time, mid-season, with no remaining levers takes considerably longer to recover from.
About the Contributor
Mary Wiegand is the Founder & CEO of Boon, a demand planning and inventory management consultancy that works with fashion, apparel, and lifestyle brands. Mary specializes in helping founder-led brands build the planning infrastructure to make smarter buy decisions before the PO goes out.
About to place a seasonal buy and want a second set of eyes on the numbers before it goes out?
Izba works with apparel and consumer brands to pressure-test buy decisions before they're locked in.
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