Changing from monthly to 4 weekly pay, why am I paying more tax?

FeryUK

Here, I've done the calculations as well for you, to extend my reply from above: Regardless of how many hours you are working per week, at the end of the day (end of financial year in our case ) your tax is paid based on the total amount you are earning per year, regardless of how you are being paid: monthly, weekly, or every 4 weeks in your case.

As you mentioned that your salary will be £19,770, this is how things will stand for you at the end of the year, regardless of how much emergency tax you'll pay, they will have to refund you:

A simplified illustration of your tax:

You'll pay no tax on the first £11,500 that you're earning.
You'll pay £1,654 tax on £8,270 (at 20%)
You'll pay no higher rate tax
Total tax paid: £1,654

A simplified breakdown of your National Insurance:

You'll pay no NI on the first £8,164 that you're earning.
You'll pay £1,393 NI on £11,606 (at 12%)
You'll pay no second band NI (at the 2% rate)
Total NI paid: £1,393

Your hourly rate will be £10.27 if you're working 37 hours/week, and you net pay will be £1,394/month, and £321/week.
(Source: income-tax.co.uk)
Hope it helps.