Available-to-promise
Definition
Available-to-promise (ATP) is the quantity of stock a business can commit to new orders — inventory on hand minus what existing orders have already reserved — the number that prevents selling the same unit twice.
A warehouse holding 100 units of which 80 are committed to existing orders does not have 100 units to sell. It has 20. Available-to-promise is that second number, and the distinction between on hand and available is the difference between an inventory system and a stock-count field. Systems that check only on-hand quantity oversell routinely: two orders arrive for the same units, both are accepted, and one customer gets an apology.
Why it matters
Overselling is not an edge case; it is the default behavior of any system without reservations. The moment order acceptance and physical stock are checked against the same raw count, concurrent orders race each other and the loser is discovered at pick time — after the customer was promised. The fix is structural: committing stock to an order must reserve it, and every subsequent availability check must subtract reservations. Whether that subtraction is enforced in code, or left as a report someone should check, is the question to put to any inventory vendor.
How available-to-promise works in Oneop
Oneop enforces the invariant in code: available equals on-hand minus reserved, and it cannot go negative. A sales order reserving stock commits it; a second order cannot sell inventory the first already claimed, because the availability check is the same enforced calculation everywhere. This is the mechanical reason overselling cannot happen, rather than a policy hoping it won’t.
The reservation model sits inside a real warehouse system: multiple warehouses with bin-level locations, lot and batch tracking, product variants, transfers between sites, cycle counts, and RMAs for returns. Purchasing runs through purchase orders with landed-cost allocation; outbound runs through sales orders, reservations, picking and shipment, with nine carrier integrations rating and buying real labels. Inventory value posts to the general ledger at weighted-average or FIFO cost.
The cross-module proof that the number stays true: voiding an invoice releases the stock that invoice had reserved and reverses its ledger entry in the same action — availability and accounting cannot drift apart, because they are one record.
Inventory is on by default in Oneop, on every plan (Free is capped at 20 products and 1 warehouse).
Related terms: general ledger. Product page: Inventory.
Related terms
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