Please cancel, apologise to them and be nice. 

And congrats on the other offer. All the best.

At this point it seems that the best thing you can do is cancel on the day of. You could already send an email and call first thing in the morning. 

It’s definitely not better to do an interview and use more of their time if you’re not planning on taking their potential offer.

Things don’t always work out perfectly. Everybody is aware of that. Congrats on your offer and best of luck starting out!

I agree with Pedro that it is better to cancel prior to the interview rather than waste interviewers' (and yours) time.

You never know - perhaps the interviewers had to push important work to accommodate you and they will be actually glad to “recover” an hour of time during their busy day (I may or may not be speaking based on personal experience).

Or maybe one of them got sick in the meantime and your message (even at the last minute) will save everybody from panic mode search for a replacement.

Just be professional and respectful in your communication to leave a good impression.

Congrats and good luck with the offer you accepted!

Slawomir

It's better to be upfront and tell them you received a great offer than to go to an interview while having already accepted an offer.

In the first case you are being respectful and they should be cool with it. This is not as uncommon as you think, On the second case, you'll either bomb the interviews, reject an offer, and waste everybody's time (and they may find out). Which means a close door later on… and you may want to keep it open.

Of course, provide a good reason for accepting the other offer without even interviewing with them, and thank them for all the effort they'd put on you. If you do this well, you'll keep the door open.

Hey there,

I'd definitely cancel since you would just block more resources on the interview day for them.

Cheers and congrats on the offer! ;-)

Florian

Hi there,

Is the other offer signed and confirmed? With a start date very soon? 

If so, I would cancel. If so though, you need to send an email now. I would not send them an email tomorrow morning right before the interview.

Hi!

I would definitely cancel.

Congrats on your offer.

Best,

Anto

…