Trying to work out Net to Gross for £600 a week take home net wage

sitesafe

Would really appreciate some help. 
Just completed a month's temporary assignment meant to be paid at £600 net per week - rather than be employed for a month I've agreed to the client to gross it up to what it should be.  I'm just doing my own research for how much this should be on top of my take home per week of £600.  I'm on standard 21/22 tax code, no student loan etc.  I get that I'll be self employed for this and i already fill in an annual tax return.
I've tried a few of the net to gross salary calculators but some are coming up with different amounts and not sure if the NI deduction shown is correct bearing in mind I'll be self employed and it's paid at a different amount I believe.  Thank you in advance.

molerat

As an employee with a 1257 tax code and a 20% tax payer to take home £600, and not including any pension deductions or employer contributions, you would need to be paid £779 gross.

Undervalued

Remember too that a PAYE employee would get at least 28 day paid holiday per year and also at least statutory sick pay (c. 100 per week) should they be off sick for more than three days.

A self employed person gets neither.

So you need to factor this in as well.

kimwp

Moneyhelper seems to have quite a straightforward walk through of the things to consider under the article heading 

Tax and National Insurance when you’re self-employed

But the grossed up value would depend on what tax bracket you are in. So if you're earning over the 40% tax bracket, the gross up will need to include 40% tax (if it's the same as employed tax). But if you're earning less than £12500 total, there might be no tax. That might explain why you are getting different numbers from different websites.