Once you get your head around it, it isn't as complex as it seems. It took me a while to understand but doing a dummy work though following P49 helped to clarify how it all worked.
What I meant is that I will agree £5 net now,
Please don't do that. Please take our advice and agree a gross wage... do not mention about any net payment to your to-be employee.
You can use Listen To Taxman to do some calculations.
Lets do an example. For now lets say your nanny is to work 25 hours per week, and you are aiming for her pay to be 5 net per hour give or take a bit for this particular moment in time and based on a BR tax code.
So lets enter 162.47 in the My Gross Income Per Week box, and enter BR in the Tax Code box. Click calculate and you should see that for 2007/08 tax year, weekly net is £125. The tax free allowances section on the table will show as 0.00, as we are using BR tax code.
From the table you will see that Gross Pay per year, on this basis is £8,448.44.
You can now use that figure to play around with the figures so that you get a reasonable gross salary figure for use in the contract, which would result in close to your desired 5 net per hour. Perhaps £8450.00 for example.
Using Table A in the NICs Tables See CA38 (I expect Table A would be used, though it may not be, but good enough as an example)
and using Annual Gross Salary of £8450 (thus £162.50 per week), on page 11 of the CA38, you can find Table A weekly, showing the nearest lower figure as £162, so looking across the table, employers NI is £8.00
So assuming the same pay every week, then for a good guide as to how much it will cost you as employer, we take the Annual Gross salary £8450 and add (£8 * 52) £416, giving annual total of £8,866 - so to be safe budget for £9,000.
£8450 gross pay, based on 25 hours per week, is 1300 hours per year, thus £6.50 gross per hour... which is above National Minimum Wage.
I think I'll just tell her that I've calculated the gross equivalent to be £x and could we agree on that as it simplifies things for me...
Yes, do that... tell her it is £x per hour gross, or even just give a per annum figure, such as £8450 gross per year.