Most web designers will find that initial web development is usually followed by regular updates and general maintenance work.
I have a simple system: £30 an hour rate, calculated down to single 15 minute slots (i.e. it’s £7.50 up to 15 minutes, £15 up to 30 minutes and so on). I try to give clients a rough estimate of the time required but I don’t give a precise figure because it’s not always possible to anticipate complications, yet it’s only fair that I get paid for the amunt of time I actually spend on a job. That’s what you would expect from a plumber, a babysitter or a personal trainer – why should it be any different for web designers?
I look at the time when I start, I look at the time when I stop – simple as that. In fact if possible I email the client to say “I’m going to make those changes now” and then email them back when they are done, so they can see how long it took. Of course I could inflate the hours, but I don’t. Why? Because honesty is always the best policy: in the long run it gets you more work and it’s a lot less stress than lying – at least for me.
In order to keep a “tab” for each client I use a simple Excel spreadsheet template. This is already formatted with the right cell data types (date, number etc.) and with a “total” box which adds up the amounts automatically. I simply copy this blank template into the client’s folder on my computer and rename it as needed, then start filling it. Each sheet holds up to 20 entries but you will never fill them all. When the total has reached a certain amount, depending when you wish to get paid, you fire off your invoice, attach a copy of the spreadsheet for your client’s reference and archive the file. Then start another blank sheet.
You can download the template here, it saves me a lot of time and hassle and hopefully it will work for you too. If you can improve on it, by all means do and please send me your version!