How to fill in a timesheet you forgot to keep

This page assumes the honest position: it is Friday, the timesheet is empty, and the week has gone. You are not about to record your time. You are about to reconstruct it, and the question is how to do that in the way that loses least.

First, know which way you will be wrong

A reconstructed timesheet is not randomly inaccurate. It is wrong in a predictable direction, and it is wrong low.

The planning fallacy — named by Kahneman and Tversky in 1979, and measured since — is that we underestimate how long our own work takes, even knowing it has overrun before. Memory also compresses: a fragmented afternoon of six things becomes “the afternoon”, and the short pieces are the first to disappear. Since most of a working day is short pieces, most of what vanishes is real work.

So when you finish and the total looks about right, it is probably an hour or two short. Knowing that is more useful than trying to be more careful.

The order that loses least

Do not start at Monday morning and work forwards. Start with what is certain and let it hold the rest in place.

1. Fixed points first

Open the calendar. Meetings, calls, appointments and travel are the only parts of the week with times already attached to them. Put them in first, at their real length rather than their booked length — a thirty-minute call that ran to fifty was fifty.

2. Then the artefacts you left behind

You left timestamps all over the week without meaning to. This is the step people skip, and it is the one that turns a guess into something defensible:

• Sent items. Every email you sent has a time on it, and an email is usually the end of a piece of work rather than the start. Two sent at 11:40 and 12:05 bracket something.
• Modified dates. Sort the folder by date modified. Documents, spreadsheets and drawings all carry the moment you last touched them.
• Commits, tickets and comments if you work that way — the most precise record most people have and the one they forget they are generating.
• The phone log and messages. Length and time, already recorded.
• Browser history. Uncomfortable but effective. It will also show you the hour you are about to forget on purpose.
• Photographs. If you visit sites, your camera roll is a timestamped itinerary.

3. Then fill the gaps between them

With the fixed points and the artefacts in, the week is a series of bracketed spaces. Ask what each space was, in order. Some you will know immediately. Some you will not.

4. Then stop, and leave the rest blank

This is the part everybody gets wrong. When you reach an hour you genuinely cannot place, the instinct is to give it to whichever project is nearest and move on. Do not. Mark it as unaccounted.

A timesheet with four honest blanks is worth more than one that adds up perfectly, because the blanks tell you something and the padding tells you nothing. If you are billing from it, the blanks are also the difference between an estimate and an invention.

Round against yourself

When you are unsure between forty minutes and an hour, take forty. Not because you should undercharge, but because a reconstruction is already biased high on confidence and low on detail, and rounding up compounds the one thing you cannot defend if anyone asks.

Do the opposite on the unaccounted column: if you are unsure whether you lost one hour or two, write two. Being generous about what you cannot account for is what makes the sheet worth reading next month.

Write one note per entry, for the version of you who reads this later

Not the project name, which the row already has. Write the thing — "second draft after their comments", "chasing the surveyor". Six weeks later, this is the difference between a record and a list of numbers, and it is what you will need if a client queries a line.

Mark it as reconstructed, and say so if it matters

If your system lets you flag an entry as estimated rather than recorded, do it. If it does not, put it in the note.

This matters more than it sounds. Two hours you logged as they happened and two hours you reconstructed on Friday look identical in a total, and they are not the same evidence. If a client ever disputes an invoice, the difference between "my record shows" and "I believe it was about" is the whole conversation.

How not to be here next month

Nothing above fixes the cause, and it is worth being clear about what the cause is. It is not discipline. It is that recording time asks you to do something at the moment you are busiest, and depends on you remembering to do it.

Three things that survive a bad week, in order of how much they help:

1. Shorten the gap. Friday to Monday is a reconstruction. Same-day is mostly memory. Within the hour is mostly a record. Nothing else you change matters as much as this one.
2. Make the unit smaller. Filling in one line about the last hour is a thing you will do. Filling in a week is a thing you will postpone, which is how you got here.
3. Stop relying on remembering. Whether it is a recurring alarm, a sticky note, or software that asks, the point is the same: take it off your memory, because your memory is already fully committed.