Timekeeping best practise

I’m a self-employed freelancer. I set up an Excel file for each of my clients. One worksheet covers one month, with vertical columns for the date, the task, hours worked per day (9:00-2:30 for example), and notes.

Horizontally, I divide the month up into weeks, and I have a running subtotal for hours worked per week, and hours worked per month, and is one (nice!) case, hours worked per year.

I bill in 15 minute increments.

Sometimes I submit the Excel file with my bill, depending on the client and the kind of arrangement we have - ongoing vs. short term, hourly vs. a set fee, etc.

I keep a file like this even if I am working for a set fee, so I can see how good (or bad!) my estimate was.

Works for me.

All of the designers and engineers are required to track their time to the nearest .25 hours using Quickbooks Pro. The numbers are used to evaluate the projects by phase and occasionally to generate billing reports.