Reading sell-through and markdown risk in a seasonal buy when your supply chain just got shorter

The Panama Canal is cutting vessel slots again. The new administrator confirmed in September 2026 that reservoir levels have dropped further, and the simultaneous strain on Red Sea and Gulf shipping lanes from Iran-war disruptions means carriers are rerouting through the Cape of Good Hope or queuing for restricted Canal access. For a CFO at an apparel brand or retailer, this is not a logistics headline. It is a margin event. Transit times from Asian manufacturing hubs to US East Coast ports, which were normalising toward 28-32 days post-Covid, have stretched again toward 45-52 days on some lanes. When product arrives late into a seasonal window, the weeks of full-price selling contract, and the probability of hitting planned sell-through rates drops before a single unit hits the floor.

The mechanics are straightforward and brutal. A holiday sweater collection planned for a 14-week selling window at full price now lands with 9. The open-to-buy math changes. The markdown liability the finance team booked as a contingency reserve starts looking undersized. If you built your seasonal buy on historical sell-through curves from periods with reliable lead times, those curves are no longer the right baseline.

The playbook: from buy approval to end-of-season close

Step 1: rebuild your sell-through model around compressed selling periods

Pull your most recent two seasons of weekly sell-through data, segmented by channel (own retail, wholesale accounts, e-commerce) and by category (outerwear behaves differently from accessories or basics). Reindex each season to weeks-remaining-in-window rather than calendar week. A coat that sold 60% through by week 6 of 14 is not the same sell-through story as 60% through by week 6 of 9. Your regression line for markdown timing needs to use the compressed window as the x-axis.

For wholesale, this matters even more. Nordstrom, Bloomingdale's, and specialty accounts take markdowns on a defined schedule. If your goods arrive in week 3 of their selling window instead of week 1, you have already missed their first turn cycle. The buyer will not extend the window; they will accelerate the markdown and charge you back for the differential. Model that explicitly. It is a receivable impairment risk, not just a margin variance.

Step 2: build a three-scenario markdown reserve at the time of buy approval

Most apparel finance teams reserve for markdowns as a percentage of cost, reviewed quarterly. That cadence is too slow when lead times are volatile. At buy approval, build three explicit scenarios:

The base case uses your reindexed sell-through curve with the most likely transit time. The stress case assumes a further 10-day delay (a second vessel rerouting or a customs clearance backlog at Long Beach or Savannah). The floor case models arrival so late that only the final four weeks of full-price selling remain, which for most seasonal categories means you will clear through an off-price channel at 30-40 cents on the cost dollar.

Attach dollar values to each scenario and present them to the board with the buy recommendation. This is not pessimism; it is accurate capital allocation. A CFO who surfaces a $4 million markdown exposure at buy approval has far more options than one who surfaces it at the weekly business review in week 8.

Step 3: instrument your in-season triggers

Define in advance the sell-through thresholds that trigger action, and tie them to specific weeks in the compressed selling window. A common framework: if you are below 35% sell-through by the halfway point of the full-price window, a markdown is likely unavoidable and earlier is cheaper. Below 20% at the halfway mark, you are looking at off-price liquidation and should be calling your TJX or Burlington contact now rather than in six weeks.

Assign an owner to this number. The merchant will defend the price. The CFO's job is to be the one who actually reads the curve and pulls the trigger on the reserve adjustment. Waiting for consensus is how brands end up with $80 units moving at $18 in January.

Step 4: renegotiate cost terms where lead time risk shifts to the vendor

Some vendors will absorb part of the transit-delay risk through extended payment terms or shared markdown funding, particularly if the delay stems from port congestion rather than your own order placement timing. This is a CFO-level commercial negotiation, not a merchandising one. If a vendor in Vietnam or Bangladesh shipped on time but the goods are delayed by 18 days due to Canal rerouting, document the carrier's confirmation and use it in your cost negotiation. Markdown funding at 3-5% of the invoice value is not unusual where causation is clear.

Also revisit your landed cost model. Cape of Good Hope routing adds roughly $400-600 per container in fuel and charter premium on current spot rates. For a container of knitwear at a $12 cost average, that erodes 2-3 points of gross margingross marginGross margin is the share of revenue left after subtracting the direct cost of producing goods or services, expressed as a percentage of revenue.View full definition → before the goods touch your DC. Update your standard cost cards now.

Pitfalls that sink otherwise competent teams

The most common failure is treating the seasonal buy as a merchandising decision with finance signing off on the OTB. It should be an underwriting decision. Finance owns the markdown reserve, which means finance must own the assumptions behind it.

The second failure is allowing the size curve to stay intact when delivery is late. If a full delivery arrives three weeks late, you do not need the same depth in your opening sizes. You need a tighter curve weighted toward your fastest-moving sizes, because you will not have time to reorder into gaps. Approving a late delivery at full purchase quantities without adjusting the size curve is a structural sell-through problem from day one.

Watch also for duty classification risk compounding the timing problem. A garment that crosses from CN 6110 to 6211 because a trim change was made to accelerate production can shift HTS classification, triggering a different Section 301 duty rate. Finance teams running tight on cash after a margin squeeze are not always the ones catching a misclassified import that costs 12 points in unexpected duty.

Quick wins to start this week

• Pull your in-transit inventory report and reforecast your selling window for every seasonal SKU currently at sea, using actual ETAs from your freight forwarder, not system-booked dates.
• Add a "weeks of full-price window remaining at arrival" column to your open-to-buy dashboard and flag anything below eight weeks for immediate markdown reserve review.
• Check your markdown allowance language in your top five wholesale contracts. If it does not cap the retailer's markdown timing trigger, you have unquantified liability sitting in deferred revenue.
• Brief your logistics team to document any Canal or rerouting delay with carrier confirmation so you have the paper trail for vendor markdown funding conversations.

The sell-through curve does not care about geopolitics. It just tells you whether you bought the right amount for the time you have left. Right now, in September 2026, apparel CFOs have less time than their buy plans assumed. The ones who reforecast that exposure today will spend less money fixing it in January.

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