Every time a big campaign is coming, your heart skips a beat
Have you ever run into this? Sales surge during a sale season, but your best-selling item sells out on day one. Customers can't place orders, so — afraid of running out next time — you over-order to be safe, and end up with inventory sitting in the warehouse for more than a quarter, turning into sunk cost that generates no revenue.
The question every seller wants answered is: how much stock is just enough — enough that you don't run out and lose sales, but not so much that your capital gets locked up in boxes that won't sell. Let's look at the guiding principles.
Why 'guessing' is dangerous
Restocking on gut feeling carries 2 risks that quietly eat away at your profit:
- Stockout: You lose sales on the day traffic is highest, and your shop score and product ranking may drop because the system sees the item as unavailable.
- Overstock: Capital gets frozen, storage costs rise every day, and you risk goods deteriorating or going out of fashion — especially in the fashion and food categories.
The solution isn't to guess more accurately, but to set up a calculation system based on real data.
5 steps to calculate just the right restock quantity
1. Find the baseline sales for each SKU
Start by looking at the average daily sales during a normal period, broken down by individual SKU — not the shop total — because each product sells at a different rate. For example, the black t-shirt (SKU: TS-BLK-M) sells an average of 10 units/day, while the yellow one (SKU: TS-YEL-M) sells 3 units/day — this baseline figure is the starting point for every calculation.
2. Multiply by the campaign accelerator
During a big campaign, sales often surge several times over. Look at your past campaign statistics to see how many times sales grew compared to a normal day, then use that as a multiplier. A simple estimation example:
| Product tier | Approximate accelerator | Example SKU |
|---|---|---|
| Hero product (headliner) | x4–x6 | TS-BLK-M |
| Secondary best-seller | x2–x3 | TS-WHT-L |
| Long-tail product | x1–x1.5 | TS-YEL-M |
These numbers are just a starting framework — adjust them according to the ad budget and discounts you'll actually invest, because the harder you push, the more sales bounce up.
3. Add safety stock
Buffer for unexpected volatility at around 10–20% of your forecast, focusing the buffer mainly on hero products that you can't afford to run out of. Long-tail products don't need much buffer, because running out costs fewer opportunities and they're easier to leave stranded.
4. Subtract remaining stock and incoming goods
Don't forget to count what's already in the warehouse and the lots you've already ordered from suppliers. The simple formula is:
Quantity to restock = (forecast + safety stock) − remaining stock − goods in transit
5. Allow enough lead time
Calculate backward from the campaign day: how many days the supplier needs to produce, how many days to ship into the warehouse, and how much time the warehouse needs to receive and store the goods. The goods must be ready before the campaign opens, not arriving right on the day.
When a fulfillment system helps make 'just right' easier
The big problem with calculating on your own is that data is scattered and not updated in time — especially when you sell across multiple platforms at once. A warehousing and fulfillment system like Flash Fulfillment helps clarify the picture through these principles:
- Centralized stock: See the remaining quantity of every SKU in real time, with automatic stock deduction across channels, reducing the problem of overselling beyond what you actually have.
- Historical data ready to use: Review daily sell-through rates to set your baseline and accelerator more accurately — no guessing.
- Fast receiving, packing, and shipping: When goods arrive at the warehouse, the team stores them and is ready to pick and pack immediately, helping cut lead time on the delivery end on days when orders flood in.
When picking, packing, and shipping are taken off your hands, your time and mental energy are freed up to focus on marketing and choosing which products to really push.
Key takeaways
- Don't restock on gut feeling — start from your baseline sales per SKU.
- Use campaign accelerators according to each product's level of importance, not the same multiplier across the board.
- Buffer safety stock only for hero products, and always subtract what you have and what's in transit.
- Calculate lead time backward so goods are ready before the campaign opens.
- A centralized stock system keeps your 'just right' numbers grounded in real data, not guesswork.
Want to plan your restocking before the next campaign to be more on point? Explore approaches to warehouse management and fulfillment, then talk with the Flash Fulfillment team to see which kind of system suits your shop.
Frequently Asked Questions (FAQ)
How many days before a campaign should I start restocking?
It depends on your supplier's lead time and shipping into the warehouse. The principle is to calculate backward from the campaign opening day, and also allow time for receiving and storage at the warehouse, so the goods are ready to sell before the actual event — not arriving right on the day.
If I have no historical campaign sales data at all, how do I start?
Use your normal-period sales as a baseline, then estimate the accelerator cautiously at first, focusing on stocking enough hero products. For new or long-tail products, start with a small quantity and watch the sales signals in the early part of the campaign so you can restock in a second round.
How much safety stock should I buffer?
Generally around 10–20% of your forecast for products you can't afford to run out of, adjusted for the product's volatility and supply risk. Products that are easily stranded or expire quickly shouldn't be over-buffered.
Does using fulfillment really help with dead inventory?
It helps indirectly by giving you clearer visibility into stock data and sell-through rates, so you can decide on restocking more accurately than by guessing. Consolidating stock in one place also reduces the problem of goods spread across multiple locations, where some items get stranded while others run out.
