Best thing to do is phone tax credit office & explain the situation and they should be able to give you an estimated amount and would be able to answer your questions. Their phone number is 0845 3003900.
My understanding of it, is that, working out the way you have put it is not the same way tax credits work it out.
Your ex is employed for the whole of the year (52 weeks) and for the benefit of having increased holidays, she has a pro-rata'd salary.
This does not mean that she is "not in work" for those 13 weeks holidays, therefore you do not need to deduct these weeks when calculating entitlement.
She is paid an annual salary equated to 39 weeks pay
She works for 39 weeks
She is paid for 52 weeks (but only 39 weeks worth of money)
Therefore she works 17 hours per week all year round, the fact that she is at home for 13 weeks of it, has no bearing with tax credits.
Hope this helps again
You could always get it 100% by ringing tax credits as if you were the person working term time to check the entitlement, as obviously they will not discuss any other persons circumstances with you.
Mrs Bobbitt, IFIKNEWTHEN
If my head wasn't so scrambled with all this I would have phoned the tax benefits people before now so I have.
For other readers of this thread Mrs Bobbitt is exactly correct re 17 hours per week and as a single parent with two kids 11 and 6 paid about £5k x2b should get £146 pw estimate - which will help go some way to filling the hole created in setting up two households. I might actually have some cash leftover each month to buy some food for myself.
When you say you may have money leftover for some food, you seem to have forgotten another downside of working term time only (there is two, my mistake:P )
Having 13 weeks off can mean alot of spending,(window shopping becomes boring after week 2 of the 6 weeks hols) and also, being at home with the kids 24/7 means lots of......Mum, can I have? Mum, can we go....?
Something to bear in mind before you set off to spend excess cash in the supermarket!