My costs are typically around 6k a year, no sick pay, no holiday pay plus outgoings for sickness insurance, money aside for the next van, etc. If I only turned over £37000 then I'd just as well be employed for £27000 given the right job.
Many guys only look at their turnover which is great if you are fiddling the system.
Your higher hourly rate pays for your hols etc ...thats why you do not earn 8/9/10 pound per hour, thats where your holiday pay comes from amongst other stuff. Its nothing to do with "fiddling the system". And..if you have "sickness insurance", i do not have it , but i have had it before..check the details...it probably pays out for a limited period only after you have been off for so long. i.e if you have a week in bed with the Flu, or a sore arm then you'll probably be getting nothing.
Its a foregone conclusion that an employed person will generally work 11 months of the year as they have 1 months holiday as a legal requirement. If like Daz says, and you're pretty average anyway..having some holidays and losing a day or two here and there it will equate to you've probably worked 10 months.
I think where you see the benefit is that you do not have to pay expenses to get to work, for some employed people them expenses are considerable. Thats a massive saving. We, as self employed pay less NI.