Guide
A simple expected-value formula tells you whether holding a slot beats booking it solid, plus how to measure your real fill rate before you decide.
Every dispatcher and owner-operator faces the same trade-off. Hold a slot open for a same-day emergency call and you might earn a fat premium ticket. Or that slot sits empty because nobody rang, and you've lost a booked job you could have had instead. There's no universal answer like "keep two slots open" or "always leave your last hour free". It depends on your numbers, not a rule of thumb someone posted in a trade forum.
The good news is this is a straightforward maths problem. You need two numbers: how often an open slot actually fills with a same-day job, and how much more you make on an emergency call versus a normal booked job. Once you have those, the decision falls out.
Expected value (EV) is what you'd earn on average if you repeated this decision many times. For a held slot:
EV of holding = (fill rate × emergency ticket) − (normal ticket)
Read it as: your fill rate tells you the odds the slot gets used. Multiply that by what you earn when it does. Then subtract what you'd have earned anyway from a normal booked job, because that's the job you gave up to hold the slot open.
If EV is positive, holding the slot beats booking it. If it's negative or near zero, book it solid and deal with genuine emergencies by triage instead — bumping or rescheduling a lower-priority job already on the board.
Say your average normal ticket is $310 and your average emergency call-out (with premium pricing) is $520. Over the last two weeks you tracked every day you left a slot open and found it filled on 60% of those days.
EV = (0.60 × $520) − $310
EV = $312 − $310
EV = +$2 per day
That's barely worth it. At a 60% fill rate and this premium, holding the slot is roughly break-even. It's not a disaster to hold it, but it's not a clear win either — you're gambling for about two dollars of expected upside, with real variance either side.
Now push the numbers a bit. If your fill rate is 70% instead of 60%:
EV = (0.70 × $520) − $310 = $364 − $310 = +$54 per day
And if you also raise your emergency premium so the ticket is $560 instead of $520:
EV = (0.70 × $560) − $310 = $392 − $310 = +$82 per day
This is why the brief's range holds: at a 60% fill rate with a $520 emergency ticket against a $310 normal one, you're looking at roughly $0 to $100 a day depending on exactly where your real numbers land. The rule of thumb that falls out of this: hold one slot when your emergency premium is 50% or more above your normal ticket and your fill rate is above 50%. Below both of those thresholds, book solid.
A big premium with a low fill rate doesn't save you. If your emergency ticket is $700 (a 125% premium over $310) but only 30% of held slots actually fill:
EV = (0.30 × $700) − $310 = $210 − $310 = −$100 per day
You'd be better off booking that slot solid every time. Equally, a high fill rate with a thin premium doesn't work either. If your "emergency" pricing is only $350 against a $310 normal job (a 13% premium) and it fills 80% of the time:
EV = (0.80 × $350) − $310 = $280 − $310 = −$30 per day
You need both conditions doing real work: enough premium on the ticket, and enough demand to fill the gap. Check your actual emergency pricing against your normal rate using a job profitability calculator — if the margin on your "same-day" jobs isn't meaningfully better than standard work once you account for the disruption, it's not really a premium worth holding a slot for.
Don't guess this number. Most owner-operators either overestimate demand ("I get calls constantly") or underestimate it ("emergencies are rare") based on memory of the loudest or most recent days.
Log every same-day request for a fortnight, whether you had a slot open or not:
Your fill rate is: (days the slot converted to a job) ÷ (days you held a slot open). Two weeks gives you 10 working days, which is a thin sample but enough to see whether you're closer to 30% or 70%. If your trade has strong seasonal or weather-driven spikes — plumbing in a cold snap, HVAC in a heatwave — track a fortnight in your normal season and a fortnight in peak, because the fill rate will differ sharply and one held slot policy won't fit both.
| Fill rate | Emergency premium vs normal ticket | Decision |
|---|---|---|
| Under 40% | Any premium | Book solid, triage instead |
| 40–50% | Under 50% | Book solid |
| 40–50% | 50%+ | Marginal — track another fortnight |
| 50%+ | Under 50% | Marginal — raise your premium or book solid |
| 50%+ | 50%+ | Hold one slot |
| 70%+ | 50%+ | Consider holding two slots |
If your EV is negative, that doesn't mean you turn away emergencies. It means you don't leave a slot artificially empty waiting for one. Book the day solid, and when a genuine emergency call comes in, bump the lowest-value or most flexible job already on the schedule to tomorrow, and slot the emergency in at premium price. This keeps your calendar full on average while still capturing the occasional high-value call — you're just not paying the daily cost of an empty slot to do it.
It's also worth checking what a missed same-day call actually costs you if you turn it away entirely rather than bump someone. A missed call revenue calculator can put a number on that, which feeds back into whether triage or holding is the better default for your business.
None of this maths includes the time buffer you need for jobs that overrun. That's a different problem with a different fix: build in 15–20% slack across your working day for jobs that take longer than quoted, and treat it as non-negotiable, not something you trade off against emergency slots. Mixing the two — using your overrun buffer as your emergency slot, or vice versa — is how schedules quietly fall apart by mid-afternoon. Price your day rate properly first using an hourly rate calculator, then decide separately how much of the day is overrun slack and how much, if any, is a held emergency slot.
Don't hold a slot on instinct or because a competitor advertises "24/7 emergency service". Log a fortnight of real same-day demand, work out your fill rate and your actual premium, and run the EV formula. If it's comfortably positive, hold one slot. If it's flat or negative, book solid and triage. Recheck the numbers every season, because fill rates move with weather, local competition, and your own reputation for turning up.
The Small Business Operations Kit ($19) turns guides like this one into fill-in-once worksheets: rate card, quoting sheet, job costing, payment terms and follow-up templates.