You can see that a draft will not be ready by the agreed date. Waiting until the deadline leaves the recipient less time to adapt.
Explain the delay while there is still room to change plans. Say what is complete, what remains and when you can realistically provide it. If part of the work can arrive sooner, offer that option clearly.
Check what depends on the date
Ask whether the revised timing affects another commitment. You may need to narrow the scope, obtain help or agree on a different first deliverable. Do not assume that a later date is automatically acceptable.
Confirm the new arrangement and update anyone else whose work depends on it. If the same kind of delay repeats, review estimates or workload separately. The request for more time should give the other person enough information to decide what is workable now. Avoid promising an optimistic replacement deadline solely to make the conversation less uncomfortable; it creates another expectation you will need to meet.
