One pattern I recognise from workforce management projects is the temptation to treat every coverage problem as a scheduling problem. The forecast looks sensible. The system follows the rules. Yet the roster still puts too many people on the floor at the same time.

Sometimes the missing conversation belongs with HR and operations: does the organisation’s full-time/part-time mix fit the shape of the work? A concrete comparison makes that conversation easier.

Start with the same twenty people

Imagine a shop open 9am–9pm, five days per week. It needs ten people from 9am–1pm, eight from 1pm–5pm and ten from 5pm–9pm. These three four-hour blocks require 112 people-hours per day.

Keep the total headcount at twenty. For this fictional example, each FT employee works eight hours a day, five days a week: 40 hours. Each PT employee works four hours a day, five days a week: 20 hours. Treat every hour as paid and available for work; breaks and leave are outside this first illustration.

The ratio is by employee headcount, not by paid hours. We are comparing alternative contract structures for a future workforce plan. An existing FT employee’s contractual hours do not disappear when a slider moves.

An 80/20 team: sixteen FT, four PT

Split the FT team into eight people working 9am–5pm and eight working 1pm–9pm. Add two PT employees at opening, 9am–1pm, and two at closing, 5pm–9pm.

Opening and closing each have ten people. But between 1pm and 5pm, all sixteen FT employees are present for demand of eight. That is eight extra people for four hours: 32 surplus people-hours per day.

The team commits 144 paid hours: sixteen × eight hours, plus four × four hours. The scheduling system is respecting the assumed contract lengths. Moving the excess hours without creating a gap or changing the shift design is a policy and workforce-planning question.

A 40/60 team: eight FT, twelve PT

Now split eight FT employees into four working 9am–5pm and four working 1pm–9pm. Six PT employees cover 9am–1pm, and six cover 5pm–9pm.

Period People needed 80/20 scheduled 40/60 scheduled
9am–1pm 10 8 FT + 2 PT = 10 4 FT + 6 PT = 10
1pm–5pm 8 16 FT = 16 8 FT = 8
5pm–9pm 10 8 FT + 2 PT = 10 4 FT + 6 PT = 10

The 40/60 mix covers the same demand with 112 paid hours and no surplus. Headcount is still twenty. FT employees provide 64 of the 112 hours—about 57.1% of paid hours, despite representing only 40% of the people.

Why not go further to 20/80?

Because in these shift patterns only FT employees cover the middle of the day. Four FT employees and sixteen PT employees still cover the edges, but leave four people missing for four hours in the middle: sixteen uncovered people-hours.

That is what makes 40/60 meaningful here. Eight FT people are needed for middle demand of eight; eight out of twenty is 40%. It is the lowest-wage fully covered mix among the eleven tested ratios when both groups have the same hourly wage, PT staff can cover both edge periods, and no higher FT policy floor applies.

Change middle demand to twelve and the answer becomes 60/40. Limit PT availability, add a skill requirement or change wage assumptions and the result may change again. Different shift patterns or weekly arrangements need a wider roster analysis.

Try the FT/PT conundrum in the Little Lab → Compare the actual shifts, move the ratio, then try to break the 40/60 answer.

Follow the hours into the budget

At an illustrative $30 per hour for both groups, repeating the day five days per week for 52 weeks gives:

Mix Paid hours/day Surplus hours/day Uncovered hours/day Modelled annual wages
80% FT / 20% PT 144 32 0 $1,123,200
60% FT / 40% PT 128 16 0 $998,400
40% FT / 60% PT 112 0 0 $873,600
20% FT / 80% PT 96 0 16 $748,800

The difference between 80/20 and 40/60 is $249,600 per year in this model. It comes from fewer contracted hours, not a lower PT hourly rate. The cheaper 20/80 figure does not provide the same service coverage.

This is a comparison of possible contract commitments, not an immediate saving from an existing workforce or a recommendation to replace employees. Contract obligations, employee preferences, consultation, recruitment and training all matter. The illustration excludes breaks, leave and relief coverage, penalties, overtime, wage on-costs, skills and work outside trading hours. A seven-day store needs a proper weekly roster.

Before calling the overlap waste, check the work

Are those middle hours needed for replenishment, training, stock handling or handovers? Does skill or supervision coverage explain the apparent excess? Does the spare capacity help when someone is absent?

If the work is real, make it visible in the labour requirement. If the overlap has no identified purpose, investigate the policy and contract mix as well as the roster.

I would bring HR, operations and workforce planning together to agree the demand by interval, the contract constraints, dependable PT availability and the FT presence needed for continuity. Test representative weeks and listen to employee preferences before treating one tidy day as an answer for the whole organisation.

The useful target is a mix that fits the work and the people—not a universal 40/60 rule. Where does your organisation draw the line between a scheduling issue and a contract-policy issue?