To ask if you have a self assessment tax bill of this, whether you must have earned a lot?

It might also include annual allowance pensions tax - because of the way the calculation works for how DB pensions increase in value people in defined benefit schemes can sometimes end up owing quite a bit of tax without their earnings being massive.

In answer to OP's initial question about a self assessment indicating a high income, I fill one in, on my 90 year old Mum's behalf, every year.

She is not on a high income. She has a state pension, a very small occupation pension, some savings and a few shares. What appears to have triggered the need to do a self assessment is that she receives a tiny (she left that country at 23) state related pension from her country of origin. HMRC lump this in with the 'foreign income' category thus requiring a return.

Some people have suggested I should contact them because it can't be cost effective to process the return. However, my view is that engaging with HMRC in this way is likely to involve a pile of effort on my part, and, anyway, the return means she gets a small tax rebate every year (I literally have no idea why).

So no, a self assessment doesn't mean a high income, it just means there's probably some form of non PAYE income involved, even if it is very small.

Having just filled out my own self assessment as a self employed person the way hmrc communicates your tax calculation is a bit shit - the first thing you see is how much you owe for Jan, but this will not take into consideration any tax you have already paid and also includes payment for the following year (calculated under the assumption you will earn same as this year), and is almost always more than is actually due in Jan. I always have a bit of a heart attack as it is such a large number.

in reality, I have already paid the last year’s tax, but that only gets credited 3 days after I submit the form. If this year’s income is tracking lower than last you can also ask to reduce what you pay in advance.

As others have pointed out as a rough calculation you need to earn around c£185k to be paying £70k in tax if it was all from employment.

But you pay self assessment tax in 2 payments in January and July. So this might only be half their tax bill.

If this is someone complaining about having to find £70k to pay their tax at the end of January then yes they have earned a lot at some point but that might have been an exceptional year. But that doesn’t mean they’ve kept enough cash around to pay it. If this is the case they should have been more switched on and kept the cash but to be honest lots of people who should know better don’t and it’s not an uncommon problem.

Really dependson how they pay tax. If employed and on paye and an additional 70k then someone has either messed up a tax code or there's been some other asset disposal or similar
If self employed or not on paye then could be different story

Some of it will be under payment from the current tax year and some payment on account towards the next tax year and it may not take into account payments paid on account from last year, so can look too high.

That's very possible. The assumption is that you earn roughly the same each year, so the calculation will include all of the 23-24 tax year, say, plus a payment on account (half as much again) for the year 24-25.

So it could be £50k due for this year (which has already been paid) plus £25k for next year.

No, you are wrong if it's their first one. As half of it will be on account, it could easily be only 100k or so.

1/2 of it could be on account - but still would be a decent income

If the person is a director and receives dividends, and/or is self employed, which seems likely, the tax liability to be paid by 31st Jan can include a significant account of next year's tax to be paid upfront/on account, so it could very well include this.

But a tax return wouldn’t be an indication of how much child maintenance is due. The tax calculation may not all be from income.

It wasn’t meant to be critical at all? If you have kids you should pay for them!

Self assessment covers a lot of tax alongside income tax.

Normally most people pay income tax via PAYE. Some people - self employed, variable earnings, etc etc do it through the self assessment route.

It also covers capital gains tax, so for example if he'd sold a house that he was renting out capital gains tax would he due.

Some of it will be under payment from the current tax year and some payment on account towards the next tax year and it may not take into account payments paid on account from last year, so can look too high. It does sound like a lot and implies a lot of income from somewhere, but this year may be an exceptional year so doesn't necessarily mean a regular income that high. It could also have been over estimated, is the person concerned happy the amounts are correct?

I always get caught with extra payments because I don't have a lot of PAYE income, but nothing like that amount, and the amount I actually have to pay by January is always initially over estimated by the payment on account from last year.

Honestly, the lack of thinking here is terrible sometimes. Maybe the OP is just nosey, maybe there's a partner swearing that he earned next to nothing last year and can't afford to put the hesting on or pay the nortgage, maybe it's an ex saying he can't afford child maintenance.

Absolutely, I hope whoever may or may not have deprived their child of proper support gets their comeuppance.

Might be a one off where they disposed of a house or piece of land that wasn’t their main residence which had gone up in value a lot.

but yes in general it’s not unreasonable to think someone with that sort of tax bill is quite wealthy.

Well if you've inherited properties and had to sell it in the same year, your tax bill could be this and your income less than 10k

Child maintenance no doubt

I have my suspicions pegged on a child maintenance thing.

I imagine it's her soon-to-be-ex