A retainer buys access to capacity, not only used hours
Hourly billing charges for measured work after it happens. A capacity retainer reserves a defined part of the coming month, often with response rules or priority access. The sustainability test should therefore use reserved hours, even when average delivery is lower.
Multiply the internal floor by reserved hours to find the capacity floor. Then compare the retainer fee with that boundary, the effective rate across reserved hours, and the effective rate at expected usage. These views prevent low usage from disguising an underpriced promise of availability.
Capacity test
Compare retainer economics
Use expected usage for context and reserved capacity for the floor.
Worked example: 40 hours held, 30 expected
A client reserves 40 hours each month while expected delivery is 30. A $100 floor makes the reserved-capacity boundary $4,000. A $4,200 fee protects that boundary by $200 and equals $105 across all reserved hours.
If the client uses 30 hours, the observed delivered-hour rate is $140. The hourly alternative at a normal $125 quote would be $3,750. The $450 difference pays for the ten additional hours kept available, not for work that mysteriously became more valuable.
- Capacity floor
40 x $100 = $4,000Reserved time is the binding denominator.
- Retainer rate
$4,200 / 40 = $105/hrThe fee remains above the annual floor if all capacity is used.
- Usage context
$4,200 / 30 = $140/hrThis observed rate changes with usage and should not set the contract boundary.
Define what reservation means
State the monthly hours, permitted work, response window, scheduling process, overage rate, rollover policy, expiration, cancellation notice, and whether unused capacity can be reassigned. Without these limits, the client may interpret a retainer as unlimited access.
A deliverables retainer behaves differently from a capacity retainer. If the client buys a fixed set of monthly outputs, estimate those outputs like repeated projects and control changes to the package. Do not describe deliverables as hours unless both parties actually manage the relationship that way.
Use collection history, not wishful usage
The model assumes the fee is collected and the reserved hours are genuinely unavailable to other work. It does not account for rollover liabilities, late payment, rush requests, unused time that you successfully resell, or legal rules that may affect the arrangement.
Review actual used hours, requests, response demands, and operating time every few months. If usage routinely exceeds the reservation, change the package. If the client rarely uses the capacity and does not need priority access, hourly or project billing may be clearer.