Can anyone help with child tax credits?

[LumpySpaceCow]

Hi!
I've never claimed them and was after some advice.
I have had two babies quite quickly and my childcare costs are high when I go back to work (I also have an older child). As I have had a lot of maternity leave, my past couple of years wages have been pants and the calculator online suggests that I may be entitled to some help with childcare.
What concerns me is that my previous wages do not reflect my actual income. Are the credits always worked out on previous year's wages? I don't want to apply and then get stung when I return to work!
I also pay for childcare vouchers, so am I right in saying that when I am completing the claim form I say that my childcare costs are less the 243 voucher I.e. What I would be paying in cash each month after the voucher?
I just don't want to apply and then get stung in a few years time!
Thanks!

Anyone?

You have to reconfirm your details including salary every year for tax credits so you won't get stung in a few years time if you go back to work. I think you're right that it does go on the previous year's income.
I don't know the answer to your question about childcare vouchers, sorry.

Yes you need to knock off the 243.
Yes it uses previous years income but there's only a 2500£ disregard now so if your income goes up by more than this amount then you could face having to repay large amounts!

I don't think you can claim the childcare element of tax credits as well as childcare vouchers.

Mind you I'm no expert, so you may want to phone and check.

Regards to vouchers, you must not include any childcare cots you pay for with vouchers when doing tax credits, only the costs you pay without vouchers.

Regarding your income, you have to put previous years, so 15/16 income, on the form, but if you know your 16/17 income will be higher then call them or update online once you have a claim with a new estimate, this allows the system to pay you correctly. If you're working 30+ hours a week with 2 kids you could earn up to £32,000 in the house before the payments stop, and that's without childcare.

Thanks everyone! Really helpful!