The scheme has always been that its available to those that earn the equivalent of 16 hours at NMW.
The fact of the matter is that NMW has been increased such that it is now a lot more reasonable than it once was and it's pulled more jobs (that were always being paid at a more reasonable level) into NMW territory. [note the use of the word "reasonable" - it's still not a liveable wage IMO)
Your employer will have to increase your wages to the new NMW when it comes in, that much is a fact.
Therefore from April 2025, your 15 hours will earn you £183.15 per week, so £9,524 per year.
You still won't pay any income tax on that, nor any NI.
Other changes to NI means that even if NMW hadn't gone up, they'd still be paying more in NI to employ you as the government have reduced the level at which employer's NI becomes payable and increased the % they charge.
You have two options:
- ask for an extra hour's work per week.
- renegotiate your salary so that it does pay the equivalent of 16 hours NMW - this would cost the employer £635 in extra salary to you per year, plus £95 extra in employer's NI. It's an extra £0.82 per hour taking your income to £13.03 per hour instead of the NMW of £12.21.
Renegotiating your salary could mean that without further pay rises each year, you could drop out of TFC territory again, so I'd be minded to just ask for an extra hour.
Bear in mind, however, that the NMW increase will already be increasing how much they're paying you, and the change in NI also means that you'll be costing them more.
For example, if you currently earn £12 an hour, they currently pay you £9,360 per year, plus £36 in employer's NI. Total cost to them = £9,396
The increase to NMW and NI means that they'd increase your salary to £9,524 and pay £680 in employer's NI. Total cost to them = £10,204.
They're therefore already looking at a cost increase of £808 per year for someone that works 15 hours a week, so you can imagine how much their total wage bill is going to go up, especially as you say it's a charity.
If you then wanted to up your hours to 16, or renegotiate, it would cost them £10,159 in salary and £775 in NI = £10,934, so a further £730 for one hour's extra work.
I'd definitely ask, but with impacts like that, I wouldn't be surprised if they said no.