Sales velocity is simply how fast a product sells — units per day. It's the single most important number in inventory forecasting, because everything else (reorder point, safety stock, how much to buy) builds on it.
The sales velocity formula
Sales velocity = units sold ÷ number of days
Sold 150 units of a product over the last 30 days? Velocity = 150 ÷ 30 = 5 units/day.
Choosing the right time window
- 30–60 days works well for most products — recent enough to reflect current demand, long enough to smooth out daily noise.
- Shorten the window for fast-moving or trending items so the number stays current.
- Watch seasonality. A window that spans a spike (e.g. a sale) will overstate normal velocity — exclude one-off events where you can.
Turn velocity into decisions
Once you know velocity, two things fall out immediately:
- Days of stock left = current stock ÷ velocity. (100 units ÷ 5/day = 20 days.)
- When to reorder — feed velocity into the reorder point along with lead time and safety stock.
Why automate it
Velocity changes constantly as demand shifts, so a number you calculate today is stale next week — and doing it for hundreds of SKUs by hand isn't realistic. Foreshelfrecalculates sales velocity for every product automatically from your Shopify history and shows the days of stock left and the suggested reorder quantity, updated as you sell.
FAQ
How much history do I need?
Even a few weeks gives a usable velocity; the more history, the more stable the number.
What about brand-new products?
With little history, start with a conservative estimate and let velocity settle as sales come in.