Available to Promise
Available to promise (ATP) is the quantity of a SKU that can still be committed to new customer orders by a given date, calculated from on-hand stock and scheduled receipts minus existing commitments.
Why it matters for ecommerce brands
Available to promise is the number your storefront and marketplaces should show as sellable. On-hand counts include units already sold, on hold, or damaged, so publishing them causes overselling and cancellations. ATP also lets you sell confirmed incoming stock without overcommitting. For example, 500 units on hand plus 300 arriving, minus 120 allocated and 30 on hold, gives 650 units you can promise. Selling against all 800 would create 150 orders you cannot fill on time.
Formula and calculator
ATP = on-hand + scheduled receipts in the window − allocated to open orders − units on hold
Common questions
- What is the difference between on-hand and available-to-promise inventory?
- On-hand is everything physically in the warehouse. Available to promise subtracts units already allocated to open orders or on hold and can add confirmed incoming receipts, so it reflects what you can actually sell.
- How do you calculate available to promise?
- Add on-hand stock and receipts scheduled in the window, then subtract units allocated to open orders and units on hold. 500 + 300 − 120 − 30 gives 650 units.
- Is ATP calculated in the OMS or the WMS?
- Usually in the order management system or ecommerce platform, which sees orders from every channel. The WMS supplies the on-hand and hold quantities.