Shopify Sales Velocity: How to Calculate and Track It

Sales velocity is how many units of a product sell per day or per week. It is a core input to reorder decisions: it tells you how long your current stock will last and when the next order has to go out.

What sales velocity is

Sales velocity measures the number of units sold per unit of time, usually per day. Measure it for each variant (each size, color or pack), because that is the level at which you hold stock and place orders.

With a dependable velocity figure per variant you can estimate when each one will run out, set reorder points, notice demand speeding up or slowing down, and decide where purchasing money should go. Without it, reorder timing can end up resting on how full the shelf looks.

How to calculate it

Step 1: choose a measurement window

The window changes the answer. A very short window lets one promotion or one viral post dominate the number. A very long one averages across a change in demand and hides the current rate.

A window that is a multiple of 7 days, such as 28 days, contains every weekday the same number of times, which matters if weekends sell differently from weekdays. If your catalog is seasonal, shorten the window around seasonal transitions and compare against the same weeks a year earlier (see seasonal inventory planning).

Step 2: total the units sold per variant

Export your orders from Shopify to CSV for the window and sum the quantity sold for each variant. Decide how to treat cancelled orders and returns, then treat them the same way every time. For estimating demand, it usually makes sense to leave out cancelled orders. Divide each total by the number of days in the window.

Step 3: adjust for days out of stock

Skipping this step is an easy way to get velocity wrong. If a variant was unavailable for part of the window, dividing by calendar days understates demand: you only sold what you could while it was in stock.

The adjustment assumes demand on the unavailable days would have matched demand on the available days. That is an approximation. If a variant sold out because of a one-off surge, the days it was available may overstate normal demand. If it was in stock for only a few days, the estimate is noisy, so widen the window or use a longer history.

Smoothing a noisy number

Velocity moves around from week to week. Two standard ways to steady it are the simple moving average (the window method above) and exponential smoothing, which gives recent periods more weight.

Here α is a number between 0 and 1 that you choose. A higher α reacts faster to recent sales; a lower α changes more slowly.

Using velocity to decide when to reorder

Two calculations are the starting point for day-to-day reorder decisions. The first is days of cover: how long the stock you have will last at the current rate.

The second is the reorder point: the stock level at which you place the next order.

Safety stock is the extra buffer, in units, that covers demand or supplier delays running above plan. A simple version is a fixed number of days of cover (daily velocity × those days). A statistical version is covered in the safety stock formula guide, and the full method is in the reorder point formula guide.

Compare the reorder point to your inventory position (units on hand plus units already on order, minus units committed to customers), not just on-hand units. Otherwise you will keep triggering new orders while one is still in transit. Because the reorder point moves with velocity, recalculate it regularly instead of leaving it as a fixed number.

Reading velocity trends

A single velocity figure describes the recent past. The direction it is moving gives an early signal of problems or opportunities.

Signs of acceleration

• Several consecutive weeks of increase looks more like real growth than a one-week spike. Raise reorder quantities cautiously and keep watching.
• A sudden jump deserves a cause check before you change long-term assumptions: a press mention, a social post, a promotion, a price change, or a restock after a stockout.
• A seasonal ramp that starts earlier than last year is a reason to move your seasonal purchasing forward.

Signs of deceleration

• A gradual weekly decline can mean the product is near the end of its life, competition has increased, or the season is ending. Reduce order quantities and plan clearance early (see dead stock management).
• A dip after a promotion can happen because some demand may have been pulled forward. Use the pre-promotion velocity as the baseline for the next reorder rather than reacting to the dip or the peak.
• Several related products slowing together points to a shared cause, such as season, price, traffic or a listing problem, rather than a problem with each product.

To make this routine, choose a threshold for review. For example, flag any variant whose latest week differs from its trailing four-week velocity by more than 20% in either direction. The right threshold depends on how volatile your sales are.

Allocating stock across locations

If you stock inventory in more than one place, velocity is a sensible basis for splitting a shipment. Shopify tracks inventory per location, so each location can have its own velocity.

A proportional split is a starting point. In practice, also account for what each location already holds, because the goal is roughly equal days of cover across locations, not equal shares of the new shipment. See multi-location inventory management for more.

Common mistakes

• Ignoring days out of stock. It understates demand, which leads to orders that are too small, which leads to another stockout.
• Choosing a poor window. A window that is too long smooths away a recent change in demand; one that is too short is dominated by noise.
• Measuring at product level instead of variant level. Say a product sells 50 units per day across 20 variants. That averages 2.5 per variant, and in reality the split is rarely even. Reorder decisions have to be made per variant.
• Using promotional velocity as the baseline. A discount can lift sales well above normal. Planning the next order from that peak leads to overstock. Track organic and promotional velocity separately where you can.
• Not tracking slow movers. Say you hold 30 units. At 0.3 units per day that is 100 days of cover. If velocity falls to 0.1 per day, the same stock is 300 days of cover and the cash is tied up quietly.
• Mixing units of time. Keep velocity, lead time and safety stock in the same unit (days, or weeks) throughout.

A simple review routine

• Weekly: recalculate velocity and days of cover for every variant, starting with your highest-revenue items (see ABC analysis). Compare against last week and the same week last year, and investigate anything past your review threshold.
• Each reorder: check the reorder point against current velocity, and check that lead time still matches what your supplier actually delivers.
• Monthly: review which variants are accelerating or decelerating, then set purchasing budgets and clearance plans to match. Velocity is also the raw material for inventory turnover and the other measures in the inventory KPI guide.

Velocity is a backward-looking average. When you need to plan beyond the next lead time, add trend and seasonality on top of it; the demand forecasting and forecast accuracy guides pick up from here.