October 6, 2026
Planning peak stock is a bit like catering a party when you don't know how many people are coming.
Order too little and the food runs out an hour in, with guests going home hungry and quietly deciding not to come next time. Order too much and you're eating leftovers for a fortnight, with a fridge full of money you can't spend on anything else.
Most founders handle that tension by picking a number that feels about right and hoping. It's an understandable approach, because the honest answer to "how much stock do I need for Black Friday?" is that nobody knows. Not you, not your ad platform, not your logistics partner.
But "nobody knows" isn't the same as "nobody can plan". The founders who come out of peak in good shape aren't the ones who predicted demand perfectly. They're the ones who worked out how wrong they could afford to be, and bought accordingly.
A single forecast gives you a single number, and a single number will be wrong. A better approach is to plan for a range and decide in advance what you'll do at each end of it.
That matters even more if you're building in public. Your audience can see the sale coming, and so can your competitors. Running out of your hero product on day two is visible to everyone, and so is a warehouse full of unsold stock in January. Both are survivable. Neither is something you want to be surprised by.
Must-Do Action:
Stop asking "what will demand be?" and start asking "what happens to my cash and my customers if demand is half what I expect, or double?" Plan for both answers before you place a single order.
For each hero product, build three simple scenarios.
Base case: what you'd sell if the sale performs roughly like a strong version of last year, or your best recent promotion.
Stretch case: what you'd sell if your ads, email and social all land well at the same time.
Wildcard: what you'd sell if something goes properly right, such as a creator picking it up or a post going unexpectedly big.
You don't need sophisticated modelling for this. Take your normal daily sales, multiply by the uplift you've seen in previous promotions (or a cautious guess if you have no history), and multiply by the number of days in your peak window.
Here's an illustrative example. These numbers are made up, so swap in your own.
Daily unitsOver a 10-day windowCash needed at £8 per unitNormal trading40400£3,200Base case (2x)80800£6,400Stretch case (3x)1201,200£9,600Wildcard (5x)2002,000£16,000
Now you can see the decision for what it is. Buying for the base case costs £6,400. Buying for the stretch case costs £9,600, which is £3,200 more in cash. Buying for the wildcard costs £16,000, which for many brands is more than the whole campaign is worth.
Worth-Trying Tactics:
Use your own data where you have it. Look at your best week from the last twelve months and the lead-up to it, since that shows you what a genuinely strong promotion does to your orders and how quickly it builds.
You don't need the same level of cover on everything.
Most brands find that a small number of products drive most of their peak sales. Those are the ones where running out hurts, so they're the ones worth buying deeper on. The rest of the range can usually sit closer to the base case, because the cost of a stockout on a minor product is much smaller than the cost of cash tied up in forty slow-moving lines.
Must-Do Action:
Rank your products by how much of your peak revenue they're likely to drive. Buy towards the stretch case on your top few, and the base case (or lower) on everything else.
Worth-Trying Tactics:
For long-tail products you're unsure about, consider leaving them out of the headline offer. A product that isn't in the sale doesn't need peak-level stock.
Cash isn't the only constraint. Time is, and it's the one founders most often underestimate.
Stock you order today has to be made, shipped to your warehouse, received, checked in and put away before it can be picked. If you use a 3PL, there will be an inbound deadline for peak, usually well before the sale begins. Miss it and your stock can arrive too late to be available on the day, however carefully you calculated the quantity.
Work backwards from your sale date:
When does the sale go live?
When does stock need to be received and available to pick?
How long does your logistics partner need to process inbound at peak, when everyone else's stock is arriving too?
How long does your supplier need, including any delays you'd rather not discover in November?
Must-Do Action:
Ask your logistics partner for their peak inbound cut-off date this week, and put it in your calendar. It's often earlier than founders expect, and it's a much harder constraint than your budget.
You don't have to commit everything at once.
If your supplier allows it, split your order into a committed first batch and a reserve you can trigger later. Your first batch covers the base case. The second only gets ordered if early sales are running ahead of plan, ideally with enough lead time that it still arrives before you sell out.
This is the safest route between the two risks. It protects your cash if demand is average, and it gives you a way to respond if demand is strong. It does depend on having a supplier who can turn orders around quickly, so find that out early.
If you can't split orders, the same thinking applies on a smaller scale: decide in advance what you'll do if sales are running at a particular multiple of plan, such as pausing ad spend on a product, switching the offer to a different line, or taking pre-orders.
For a more detailed way to link stock cover to your campaigns, see our guide to ad-linked buffer rules.
Worth-Trying Tactics:
Agree trigger points before the sale starts. "If we sell 30% of base-case stock in the first six hours, we place the reserve order" is much easier to act on than a judgement call made at 9am on Black Friday.
The worry about excess stock is really a worry about what happens after peak, so look at that side of the maths too.
Leftover stock isn't lost money. It's delayed money. In the example above, if you buy for the stretch case but only hit the base case, you've got 400 extra units, worth £3,200 at cost. At normal trading of 40 units a day, that's about ten days of sales. That's uncomfortable, but it isn't a disaster.
It becomes a problem when the stock can't sell through normally. Check three things:
Shelf life. Supplements, food and beauty products have dates. Stock bought for peak needs enough life left to sell in the months after.
Seasonality. Gift sets and festive packaging can be hard to shift once Christmas has passed.
Storage cost. Holding extra stock isn't free, and your 3PL's storage charges will keep running into January.
Must-Do Action:
For every product, estimate how many days of normal sales your excess stock would cover. If the answer is a few weeks and the product doesn't date, you can afford to buy deeper. If the answer is months, or the product has a short shelf life, be more cautious.
The maths is the same, but the constraints are different.
If you're fulfilling in-house, your limit is often physical: where the stock will actually sit, and how quickly your team can pick and pack it. Buying more stock than you have space or hands for can slow you down as much as running short.
If you use a 3PL, your limit is usually timing and communication. Share your forecast, including the stretch case, so they can plan space and labour. Ask about their peak inbound cut-offs, and ask what they need from you to treat your stock as a priority at peak.
Either way, your stock plan and your fulfilment plan should be written together. A 72-hour stress test is a good way to check that the two fit.
Run through this list:
I have base, stretch and wildcard numbers for my hero products
I know which products I'm buying deep on and which I'm not
I know my logistics partner's peak inbound deadline, and my supplier's lead time fits inside it
I've decided whether to split my order, and I have trigger points for the reserve
I know what my January looks like if I'm wrong in either direction
I can afford the stretch case, or I know what I'll do if I buy less
There's no perfect number, and the founders who look like they predicted peak perfectly usually just had a plan for being wrong. They knew how much cash they could afford to lock up, which products mattered most, and what they'd do when sales came in above or below plan.
That's the real aim: not an accurate forecast, but a position you can live with at either end of the range, and a plan for what you'll do next.
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