Callback inputs
Half hour intervals across a 12 hour day.
Staffing every interval for live answer with no callback.
6 fewer agents at the peak, with the callback work placed into quieter intervals.
Save or share these results
Take a snapshot of the exact inputs and outputs on screen.
Get the full Excel/VBA version
The full Excel/VBA version with live formulas, RTM tracking, and dashboards is free for now.
Results are estimates for planning purposes only and should not replace professional workforce management judgment.
The calculator staffs your day three ways using the same Erlang C engine as the Erlang C Calculator: real time only, callback aware, and the naive plan that pretends callback volume disappeared.
Step by step
- Real time only: every interval is staffed to hit the service level target on live calls. This is the expensive ceiling.
- Callback offer: when calls per interval pass the threshold, the overflow is offered a callback and the take up share accepts. Live staffing is then sized on the remaining calls.
- Callback work = accepted × (AHT + extra seconds) ÷ connect rate. Failed first attempts redial, so a 70 percent connect rate multiplies the work by about 1.4.
- Callback aware staffing: callback hours are placed into later intervals with spare capacity under the occupancy cap, and agents are added where the work lands.
- Naive plan: staffs every interval on volume minus take up, as if callbacks were free. Its backlog at close equals the callback work it ignored.
Using it well
- Tune the threshold so callbacks are offered only when waiting genuinely hurts.
- Watch the end of day: late callbacks have nowhere to go, so leave a catch-up block.
- Measure the real connect rate weekly; it moves the callback cost more than AHT does.
- Sense-check the peak with the Erlang A Calculator if callers also abandon, and the Capacity Planning Calculator for the monthly view.
Frequently asked questions
Does a callback reduce workload?
No. A callback moves the work to a later interval and usually adds overhead: dialling, voicemail, redials when the customer does not pick up. The total work goes slightly up, not down. What improves is the shape: the peak flattens, so peak staffing falls.
What is the naive plan?
Staffing as if the callback volume simply disappeared. It is the most common planning mistake with virtual hold: the callback contacts still have to be made, so the naive plan ends the day with a backlog.
Where should I set the offer threshold?
Offer callbacks when the interval is busy enough that waiting hurts, typically when calls per interval pass the level your team can answer within target. Too low and you create callback overhead all day; too high and customers give up before the offer.
Why does the connect rate matter?
Every callback that hits voicemail has to be redialled. A 70 percent first attempt connect rate means each accepted callback costs roughly 1.4 attempts of work, not one.
Related reading: callbacks move workload, they do not remove it and how AI callers are hitting your IVR.
More tools
See all toolsService Level Recovery Calculator
Behind on service level mid-month? Get the volume-weighted SL you need for the rest of the period, and see instantly if the target is already unreachable.
Open calculatorErlang C Staffing Calculator
Turn call volume, AHT and service level targets into required agents, occupancy, ASA and shrinkage-adjusted headcount.
Open calculatorErlang A Calculator
Staffing with abandonment built in: when callers give up and hang up, Erlang A sizes the team more honestly than Erlang C.
Open calculator