In my case, a ridiculously simple process which takes, at most about 15 concentrated minutes.
Why has it taken me a month?
Apart from basic procrastination issues, there's the whole "Urk, I can't remember my login number or my password" thing. This involves deciding within about 30 seconds that I'm never going to. The website is packed with helpful stuff, among which is the information that if you make three errors attempting to get into it, your account will shut down for two hours.
Decided not to risk that. Rang the tax office. As they invariably are, they were sweet, helpful and soothing. They agreed without fuss or bother, to send me a new login via snail mail.
That accounts for 6 days.
Spent a day yesterday wondering if I could claim petrol money and deciding I couldn't as ironically, I don't earn enough to offset it against any tax. Saddened by this thought, I stopped filling in the form.
Accounts for another day. 7 days.
Finished it today in a flurry of energy which took a whole five minutes - including the various "Error on this page" messages.
This means I spent at least 21 days procrastinating.
I really need to take myself in hand.