You expect a weekly report to take half an hour because writing it seems straightforward. Finding the numbers, checking them and waiting for a reply made last week's version take much longer.
Use one recent attempt as your starting estimate. Separate time spent working from time spent waiting, then include both where they affect the deadline. You may need to request the numbers a day before sitting down to write.
Record a useful comparison
After the next attempt, note the broad difference. Was the task unusually complicated, or is the original estimate usually too small? You do not need a minute-by-minute log to notice that the same preparation keeps taking an hour.
For unfamiliar work, name the uncertainty before making a firm promise. You can give an estimate after reviewing the material or agree on a smaller first deliverable. Keep estimates provisional when the conditions change. A past attempt is helpful evidence, but a report with new requirements deserves another look even if its name is unchanged.
