Every hour you track belongs to a project. A project holds its client, its rate and how it bills.
The system determines the billable rate for a time entry in this order:
A project with no rate of its own shows Inherits client rate - press Set Project Rate to give it one. Project rates are effective-dated just like client rates, so historical work keeps the rate it was billed at, and rates with invoiced time are locked.
A project bills the way its client does, the same way it takes the client's rate. Its Billing Settings (in the project panel) always shows its choices. The first follows the client and names how it bills, such as "Like Northwind (Per unit, 4 prices)"; pick one of the others for this project only, and the first again to go back. How a client's projects bill, its prices and its retainers are set on the client (see Clients). Each change saves at once.
Work that is not time is an item: a page, a fixed fee, a milestone. Click Add Item under the project's Items, or switch Log Time to Item on Track. An item is Planned (upcoming, with a date or without one) or Delivered on a day. It is earned on its delivered day, like time at a rate, and waits in Unbilled until you bill it. Open one to change it, Mark Delivered, send it Back To Planned, Settle it (you billed it outside Cesium - reversible) or delete it; an invoiced item stays as billed until its draft is deleted or its line removed.
On a fixed-fee or per-unit project the fee pays for your time, so the hours you track there are covered: they still count as worked - in Hours, Capacity and on Track, where they carry a Covered by fee tag - but they are never billed on their own. Turn on Bill extra hours to bill them at the project's rate on top of the fee; the rate then shows as Rate for extra hours. The switch is off unless the client's default turns it on. A retainer project's hours are always covered: the hours past the allowance bill only when the retainer's Bill hours over the allowance is on.
A fee project shows its Effective rate once an hour is tracked: what the work paid per hour you spent on it. A $4,000.00 fee over 50:00 hours is $80.00 an hour; a per-unit project divides what its items delivered. It is never billed and never stored. It counts the hours tracked while the project billed that way.
When a fixed fee's work runs over, the project offers three choices under its effective rate, each from today: Raise The Agreed Total (an amount and a note, kept with the day), Bill Extra Hours From Today, or Switch To Time And Materials. Every change to how a project bills applies from the day you make it; hours already tracked keep the terms of their own day, and the project then lists its terms in order.