My overheads include an office, a part-time assistant, a 911 for transport, computers, printers, scanners, hotels, restaurants, flights, specialist publications (think $500 for 50 badly written pages sometimes) client freebies, entertaining boring people when they're in town etc. etc. etc.
I work as a one-man operation but it's a business, not a part-time second job. To state the obvious: Take your billing rate (include expences if you bill that way), multiply by how much you will work for the next 12 months and deduct all your costs.
