WFM guideScheduling

Contact centre shift start optimisation

Q: How do you determine the optimal shift start times for a contact centre?

Optimal shift start times are determined by working backwards from the interval-level staffing requirement. The process: (1) Calculate the Erlang C staffing requirement for every half-hour interval in the operating day, at the forecast volume. This gives the required on-phone agent count per interval. (2) Plot the required staffing profile — this shows when staffing need is rising, plateauing, and falling. (3) Each shift start time contributes agents to the schedule from that start point until the shift ends. A 08:00 start on an 8-hour shift contributes to intervals 08:00–16:00. The set of shift start times determines which intervals can be covered and at what density. (4) Identify intervals where the schedule is consistently understaffed using the current start time set. These are the gaps that a new shift start time would fill. (5) Select the minimum set of start times that achieves the required coverage at each interval — prioritising the peaks and minimising the overstaffed troughs. (6) Test the new start time set against contractual, legal, and employee-preference constraints before implementing. The analytical output is a set of 4–8 distinct start times that together produce a staffing profile closely matching the required curve. More start times increase flexibility but also increase scheduling complexity and reduce the simplicity of the shift pattern for agents.

If the shift start times are wrong, the schedule cannot produce good interval-level coverage no matter how well the scheduling algorithm is executed. Shift start optimisation is the upstream activity — it determines the range of start times from which individual schedules are built.

What shift start optimisation is — and what it is not

What it is

•Deciding which shift start times (e.g. 07:00, 08:00, 09:30, 10:30) are available in the scheduling model
•A strategic scheduling decision that is revisited every 6–12 months or after a significant volume shift
•The activity that determines the shape of the coverage curve before individual agents are scheduled
•A constraint-setting activity — sets what is available before the scheduler chooses who fills what start

What it is not

•Assigning specific agents to specific start times (that is individual scheduling)
•Break placement within a shift (that is break optimisation)
•Shift structure design — shift length, unpaid break rules, split-shift configuration
•A fix for a forecasting problem — wrong forecasts produce wrong requirements that no start time set can fix

How to determine optimal shift start times: the five-step process

Build the interval-level staffing requirement

Calculate Erlang C for every half-hour interval in the operating day at the forecast volume. Produce a separate requirement curve for each day type (Monday, Tuesday–Thursday, Friday, weekend) if the volume pattern differs significantly by day. This is the target coverage profile that the start time set must produce.

Plot the current coverage profile

Using the current shift start time set, calculate the scheduled on-phone coverage per interval (accounting for shrinkage and breaks). Overlay this against the requirement profile. The gaps (intervals where scheduled coverage falls short of requirement) are the intervals the current start time set cannot serve adequately.

Identify the recurrent gap intervals

Focus on intervals where the coverage shortfall appears consistently — not just in one week, but as a pattern across the scheduling history. A one-off shortfall may be caused by unplanned absence or a special event. A recurring shortfall at the same time on the same day type is a structural scheduling gap caused by the start time set.

Design the minimum change set

Identify which new start time (or adjusted existing start time) would close the largest recurrent gap with the smallest disruption. Add one start time at a time, testing each addition against the coverage profile before adding the next. The goal is the minimum number of start times that produces acceptable coverage — more start times add flexibility but also complexity for agents and schedulers.

Test against constraints and implement

Test the proposed new start time set against: (a) contractual constraints — are there minimum or maximum shift windows in employment contracts? (b) legal constraints — working time regulations, rest period requirements; (c) agent preference data — if shift bidding is used, will the new start times have enough willing agents?; (d) transport constraints — does the new earliest start time require agents to arrive before public transport runs in the local area? Implement with at least 4–6 weeks' notice.

Four common coverage gaps and their start time fixes

Persistent SL failure at the opening interval (08:00–08:30)

Likely cause

The earliest shift start time is 08:00, but a significant number of agents on that start have not all arrived and logged in by 08:00. The effective available count at 08:00 is lower than planned.

How to diagnose

Pull ACD data for 08:00–08:30 and compare scheduled agents (from WFM system) against actual logged-in agents. If the gap is consistently 10%+ of scheduled count, the opening interval is being systematically understaffed by agent log-in lag.

Start time fix

Introduce a 07:45 start for a subset of agents whose role begins at that time. Alternatively, require that the 08:00 shift starts at 07:55 with a mandatory log-in check. Do not adjust the forecast — the volume is real and the staffing is genuinely short.

Persistent SL failure at 09:00–10:30 despite adequate total headcount

Likely cause

The morning peak volume arrives before the majority of shift starts. If the main shift start is 09:00 but volume peaks at 09:15–10:00, agents are ramping up (logging in, taking first contacts) during the peak rather than being fully available for it.

How to diagnose

Plot the interval-level required staffing against the scheduled staffing for Monday and Tuesday (typically highest-peak days). If the scheduled staffing line is below the required line from 09:00–10:30, the start times are too late for the peak. Compare days of the week — if Monday peaks are consistently worse, the issue is day-specific.

Start time fix

Add an 08:30 shift start for a fraction of the headcount (typically 15–25% of the peak-day requirement). This provides agents who are fully settled and available from 08:30, covering the rise of the morning peak before the 09:00 cohort begins.

Consistent lunchtime trough with agents standing by

Likely cause

The 12:00–14:00 period may have lower volume than morning or afternoon peaks, but all shift starts produce agents who are still in their active window at that time. No shift start is scheduled to end or have a break during this window — agents are all present and volume is insufficient to keep them occupied.

How to diagnose

Calculate the occupancy rate at 12:00–13:00 on an average Tuesday. If occupancy is below 70% (significantly below the operational target), the lunchtime is overstaffed relative to volume. Check whether this is consistent across days or only on Mondays/Tuesdays when morning-heavy volume patterns leave afternoon agents idle.

Start time fix

If contractual constraints allow: move the main break window to 12:00–13:00, reducing effective on-phone agents during the trough. If lunchtime volume is genuinely too low for the agent count, investigate whether a split shift structure would better match the volume profile (agents work a morning and afternoon block with an unpaid break at lunchtime).

Afternoon peak (15:00–17:00) consistently below SL

Likely cause

Most shift starts are in the morning (08:00–10:00). By 15:00, agents on 7-hour shifts are finishing or have already left. The afternoon peak is served by a reduced subset of agents with longer shift lengths, which may be a small fraction of the total headcount.

How to diagnose

Count the number of agents scheduled to be on-phone at 15:30 (a peak interval in most operations). Compare this with the Erlang C requirement at 15:30 at the forecast volume. If the scheduled count is below requirement by more than 10%, the shift start distribution is skewed too early.

Start time fix

Introduce a 10:00 or 11:00 shift start for a portion of the headcount. These agents are still available at 15:00–18:00 (on 7–8 hour shifts) when the early-morning starters have gone. This shifts coverage weight from morning to afternoon without requiring a full shift redesign.

Start time diversity vs. scheduling complexity

Each additional distinct shift start time increases coverage flexibility (the schedule can match the volume profile more precisely) but also increases scheduling complexity (more types of shifts to fill, more shift preference combinations to manage, more constraints to track). As a practical guideline:

3–4 start times

Minimum viable for an operation with a clear morning peak and standard operating hours. Works for simple 5-day-a-week operations with low volume variability.

5–6 start times

Sufficient for most contact centres with a morning and afternoon peak, weekend operating hours, or extended operating hours (07:00–21:00).

7–9 start times

Needed for 18–24 hour operations, operations with distinct day-of-week volume patterns, or blended inbound/outbound operations with different peak profiles.

10+ start times

Unusual — typically found only in very large operations with multiple channel types, multiple sites, and sophisticated WFM software. Manage complexity carefully; above 10 start times, the scheduling model may be harder to govern than it is worth.

Shift start time questions

How do you determine the optimal shift start times for a contact centre?

Work backwards from the interval-level Erlang C staffing requirement. For each half-hour, calculate how many on-phone agents are needed at the forecast volume. This produces a required staffing profile — a curve that shows when staffing need rises and falls. Each shift start time contributes a block of agents from that point forward (for the duration of the shift). The goal is the minimum set of start times whose combined contribution closely matches the required curve. Gaps between the scheduled coverage (from the current start time set) and the required coverage (from Erlang C) reveal which intervals need a new start time to cover them.