Accounting Accounting is a necessary evil for all freelance developers. You need to keep track of money coming in and going out for tax purposes. If you're billing by the hour on a job, you also need to keep track of the time you spend on billable activities. If you're not billing by the hour, you should still track your hours to get an idea of what to charge for the next fixed-price contract. Tracking your hours can be simple.
Many freelancers prefer to use a weekly planner.
I prefer to log my hours digitally because I've written utilities to write my invoices from my data files. Tracking your time when you have several customers at once can be difficult. It's something you have to decide for yourself. Checking the clock when you switch tasks covers the rest of your potential billing problems. A big time-tracking issue if you freelance at home is interruptions.