There is no universal list.
That is the annoying answer.
The useful answer is that billable time is usually work performed for a client under whatever agreement you made with them.
The agreement matters more than a generic rule.
The obvious examples
These are usually easy:
- producing the agreed deliverable
- writing
- designing
- coding
- analysis
- implementation
- consulting
- scheduled client work
If you charge hourly, this is the core.
Meetings
Client meetings are often billable.
But not always.
A sales call before the client hired you is different from a project meeting after the work began.
A contract may include meetings in a fixed fee.
The point is to be clear about the expectation.
Preparation and research
If preparation is necessary to deliver the work, there is a strong practical argument that it is part of the work.
Whether it appears as a separate line item is another question.
Again, agreement beats guesswork.
Email and small communication
This is where things become messy.
Some freelancers bill communication in small increments.
Others include normal email in the project fee.
Some only bill when communication becomes substantial.
Any of those can work.
What does not work especially well is deciding differently every time because you never thought about it.
Revisions
Revisions inside the agreed scope may be included.
Extra rounds may be billable.
This is less a time-tracking problem than a scope problem, but the time record helps show when the difference becomes real.
Internal business work
Your own bookkeeping, marketing and sales are working time.
They are usually not billable client time.
Still worth tracking if you want to understand where your week goes.
The useful distinction
Ask two questions:
Did this take working time?
and:
Should this client pay for that time?
Keep them separate.
The first is about understanding the business.
The second is about the agreement.