Pricing and capacity.
How a fixed monthly fee is calculated, what committed capacity means in practice, and what happens to the invoice when a specialist takes leave.
How capacity is priced when nobody is billing by the hour.
Hourly billing makes a simple promise and creates a complicated relationship. Every absence becomes a credit note, every quiet fortnight becomes a conversation, and somebody on your side ends up auditing timesheets instead of reviewing work.
The alternative is to agree capacity rather than hours consumed. Working hours are calculated across a full year, annual leave and public holidays are deducted, and the remainder is divided by twelve. That average becomes the committed monthly capacity written into the agreement, and the fee does not move because February is shorter than March.
What it does not do is make an absence disappear, and a provider who implies otherwise is worth pressing on. Ask what actually happens to the schedule when an assigned specialist is off for three weeks.
Where the commitment covers a whole team rather than one discipline, the arithmetic is the same but the composition question is different, and a dedicated development team covers how that is put together.