Erlang A calculator (with abandonment)

Erlang C assumes callers wait forever. Erlang A adds caller patience — modelled as average time before someone hangs up — and predicts how many will abandon if the queue gets long.

Inputs

Contacts in interval

Interval length (minutes)

Average handle time (seconds)

Average caller patience (seconds)

Mean time before a queued caller hangs up. 60–120s is typical for voice; chat patience is usually higher.

Max acceptable abandonment (%)

Target ASA (seconds) — optional

Shrinkage (%) — optional

Results

Agents required (net)—

Scheduled (after shrinkage)—

Predicted abandonment—

Mean wait (all callers)—

Probability of waiting—

Occupancy—

Offered load (Erlangs)—

Sensitivity

Agents	Abandon %	Mean wait (s)	Occ %

Erlang A is more realistic than Erlang C when queues are long and callers do hang up. Patience is typically distributed exponentially in the model; in real life it’s more complex (some callers abandon in the first 5 seconds, others wait minutes). Treat the abandonment number as an indicator rather than an exact prediction.