NT tax code IPA's
I was wondering if an IPA for NT tax code is for the exact amount of tax i would be paying if i did not have NT tax code? I have received a specific figure from my OR and the solicitors who are collecting the amount monthly . I had already explained to the OR that because i work in the building trade my weekly wage varies due to not having work or bad weather and now they are expecting a set amount per month off me. I signed the agreement believing that i would only pay whatever tax had not been taken out of my wage per month. I'm worried if i'm off work and don't get paid i will still have to pay this amount even if i don't earn the money. Can they do this? This will be on top of a separate IPA from my disposable earnings.