Maternity Leave - SMP Tax?

[MrsKT123]

Hello everyone - I wanted to see if anyone had been in a similar situation and may be able to help! :)

I received my wage slip for the first month where I'm on SMP and haven't received any additional payments from my employer and have been taxed £133.20 on the £607.88 payment (22%).

For reference, my tax code is showing as K70M1, I earn a bit over £100k and received quite a large bonus on top of this in January. Looking at this tax code it says it could be linked to a workplace benefit - I get both an employer pension and private medical insurance.

This is my first year of earning over £100k so don't need to do a self assessment until next year as I understand it.

When I looked on the maternity money website it shows I should have actually received a tax refund on top of this payment rather than be taxed on it? I haven't received any kind of rebate since I went on SMP but did have additional payments from my employer (bonus, then back-dated pay-rise).

To add, I appreciate I'm in a very fortunate position and am definitely not looking to avoid paying any tax that I owe, I just want to make sure I'm paying the correct amount as we've just moved house and planning some renovations so want to make sure I'm not overspending!

I've just found this:

The letter K is used in an employee’s tax code when deductions due for company benefits, state pension or tax owed from previous years are greater than their Personal Allowance.

Multiply the number in their tax code by 10 to show how much should be added to their taxable income before deductions are calculated.

For example, an employee with tax code K475 and a salary of £27,000 has taxable income of £31,750 (£27,000 plus £4,750).

I definitely don't think my medical benefits mean I lose all my personal allowance plus £700? I understand I lose some of it for earning over £100k but this would be paid when I do my tax return rather than PAYE. I've not had any communication to say I owe any tax either.