How often will you oversell?
Enter your stock, velocity and sync cadence. See your expected oversells per month, your revenue at risk, and concrete recommendations to reduce it — for multi-channel UK selling on Amazon, eBay, Temu and TikTok Shop.
Your setup
Enter one SKU’s operational profile. The calculator models oversell risk instantly.
Physical units available
How often stock syncs between channels
Stock held back from channels
Quick presets
Your oversell risk
Expected oversells / month
0.0
Based on 150 orders/month at this risk rate.
Revenue at risk / month
£0.35
Lost sale + avg £8 apology cost per oversell.
Stockout projection
18.0 days
90 units buyable (after 10% buffer).
Race window exposure
0.1%
Of stock cycle at collision-prone levels (W = 0.10 orders/window).
Recommendations
- Risk is already inside the healthy range (under 0.3 oversells per 100 orders). No urgent action needed.
Method: Poisson approximation of collision rate during the race window at the bottom of the stock cycle. Results are a planning aid, not a guarantee — real rates depend on burst patterns, marketplace API latency, and buyer concurrency. Observed UK seller data typically tracks this model within a factor of 2.
Why oversell risk matters for UK multi-channel sellers
On Amazon UK, an oversell triggers the order defect rate metric. Above 1% defect rate, Amazon starts suppressing Buy Box. Above 2%, account-health warnings. On eBay, oversells wreck Top Rated Seller status (which costs you the 10% final-value-fee discount). On Temu and TikTok Shop, they trigger reduced listing visibility — in the worst cases, listing freezes until the seller manually reconciles.
The three levers that control oversell risk
- Sync cadence. How often the platform pushes stock updates to each channel. Faster = smaller race window. The calculator above models the precise effect.
- Safety buffer. Stock held back from channels. A 10% buffer means Amazon sees 90 when you have 100. Higher buffer = fewer oversells but more stranded sales.
- Architecture. Whether your platform uses a single stock pool (MaxInvent) or split per-channel allocation (older tools). Split allocation guarantees stranded stock and doesn’t actually prevent oversells.
How the math works
The calculator uses a Poisson approximation for concurrent arrivals. Orders arrive at rate r per minute across all channels. In a sync window of S minutes, the expected number of orders is W = r × S. A “race window” exists at the bottom of each stock cycle where stock level is comparable to W — any new order has a non-trivial chance of colliding with another on a different channel. The collision probability during this race window is 1 − e−W × (channels − 1) / channels. The overall oversell rate is the product of the race fraction and the collision probability.
This is a planning aid. Real oversell rates depend on burst patterns, marketplace API latency, and concurrent buyer behaviour that the model can’t perfectly predict. Expect observed rates within a factor of 2 of the calculator’s estimate. Use the oversell-prevention playbook for the full operational response, including Amazon A-to-Z protection and eBay defect-rate recovery.