Road tax reminders. - mal
Non-controversial posting this time:-

Are the tax reminders late this month for renewal in March?, it doesn't give you much time if a holiday overseas is planned and it is overlooked.
Road tax reminders. - BrianW
It's only the 13th.
IIRC I normally get them around 13th to 15th.
Road tax reminders. - Dynamic Dave
I've known them arrive as late as the 23rd of the month.
Road tax reminders. - Doc
You don't need a reminder to re-tax your vehicle.
Just fill in a V10 at the Post Office and take along your registration document (V5), insurance details, and MOT if required.
Road tax reminders. - martint123
I think they're timed to arrive 2 weeks before the start of the next month as that is how early you can apply....

Any earlier and the post office get fed up of telling people they're too early..

Road tax reminders. - HF
Hmm - reminds me of the time, not very long ago at all, when I rushed in to the PO to renew my RT.

Having filled out the form, queued for ages, I was then told that I still had a month to go on my existing tax.

NOW I know that the date means the end of the month, but I didn't then. You live and learn, I guess.
HF (being very HFy at the moment, my apologies!)