When to use it
Use it any time your manager asks where something stands. Most managers want two things: how far along it is and when they'll have it. Lead with those. If there were problems along the way, mention them only if they affect the date.
Example
Manager: “How's the report coming?”
You: “It's 80% done. I'll send it Thursday.”
Manager: “Great, thanks.”
In an email or Slack message
In Slack: “Report update: 80% done, sending Thursday.” If something could change the date, add one line: “Waiting on finance's numbers; I'll flag by Wednesday if that slips.”