Physical stock answers “what units are recorded at a location?” Available-to-promise answers “what new demand may we responsibly accept?” The two quantities should reconcile, but they are not interchangeable.
Build ATP from named components
A simple current-stock model is:
ATP = eligible on hand − active commitments − policy buffers.
Eligible on hand excludes stock that cannot satisfy a new order: damaged, quarantined, under inspection, already staged for another purpose or held in an ineligible location. Commitments can include accepted orders, allocations and other reservations. Buffers cover explicitly chosen uncertainty.
More advanced ATP may include dated inbound supply and expected releases. If so, calculate it by time bucket and confidence. A purchase order expected next week does not make a unit available for a promise due tomorrow unless the business has approved that assumption.
Define every input once
Write down the source, unit, location scope, update timing and inclusion rule for each component. Determine whether the source’s “available” balance already excludes reservations. Subtracting the same commitment again understates ATP; ignoring it oversells.
Use the shared inventory article for channel-level controls and the inventory reservation guide for contention behavior.
Work through a hypothetical example
A location records 100 units on hand. Eight are damaged, five await inspection, 30 are reserved for accepted orders and seven are protected as a safety buffer. Under this model, current ATP is 50.
The location also expects 40 units in five days. A promise engine may include some or all of that supply for orders whose delivery window allows it, but it should retain the expected date and confidence. If the receipt is delayed, affected promises need an exception path.
Now suppose 10 of the 30 reserved units were already excluded from the source’s available balance. Subtracting them again would publish 40 instead of 50. Field definitions matter more than the arithmetic.
Handle multiple channels and locations
Decide whether ATP is pooled centrally, allocated by channel or capped at each destination. A centrally calculated value can improve utilization, but only if reservations and updates are timely. Channel allocations reduce contention but can strand stock.
For multi-location promises, apply product and service eligibility before summing. Ten units across locations are not equivalent to ten units at a location able to meet the order’s delivery and handling requirements.
Control future supply
Use realistic lead times, receiving capacity and inspection requirements. Do not treat a supplier acknowledgment as received stock. Record changes to expected date or quantity and identify already-promised orders affected by the change.
Consider limiting future-supply promises to approved products, channels or horizons. The operational cost of recovering a missed promise may exceed the sales benefit of publishing uncertain supply.
Recover from a wrong ATP value
Freeze or reduce publication for the affected scope when continued selling would increase exposure. Reconcile physical, reservation, allocation, buffer and inbound components separately. Correct the owning component; do not force the total to a target with an unexplained adjustment.
After correction, test one new reservation, cancellation release and channel update. Verify that stale absolute updates cannot overwrite the fresh balance.
Measure the model
Track promise failures, oversells, aged reservations, quarantined stock, late inbound supply and manual ATP overrides. Also measure lost availability from buffers and allocations. A conservative model can be safe but unnecessarily suppress demand.
Review forecasts separately from ATP. A demand forecast helps plan supply; it does not create stock that can be promised. Likewise, a high service target does not authorize including uncertain inbound. The promise policy should state which future-supply events qualify, how their confidence is assessed and what happens to accepted orders when the assumption changes.
A useful next step
For five fast-moving SKUs, calculate ATP from raw components and compare it with every channel’s published quantity. Investigate each difference using timestamps and ownership rules.
1Commerce can support inventory and fulfillment operations within configured integrations and agreed scope. Explore fulfillment capabilities or contact 1Commerce to review ATP controls.