I started this cutoff about 15 years ago.  It really took hold when I started using an online appointment scheduler (Appointy) about 10 years ago that is linked to my website.  Now I can block off all time after the last weekend in March.  Except for a few elderly the online appointment scheduler has bee wonderful to work with.

Also, on my annual Jan 1 mailing to clients I put in big bold letters about my cutoff.

Does it work?  99% today.  I will still accept open data but I try not to schedule unless you contacted me ahead and explained you were going through a medical procedure, your Guinea Pig died, etc.

I am down to a 1-man practice. My long-term employee moved away and last year my replacement who was front-line infantry in Iraq could no longer work due to being scared of Covid.  This year I had five applicants (one from Pakistan, India, North Carolina (I'm in MD) a truck driver and a waitress.  The ad said it was not a remote job.

After my cutoff for those that do want me to prepare I give them three options: go elsewhere, file an extension or I'll see if I can fit it in, but with no guarantees.  Truth is, I've never filed an individual extension because I couldn't get to it.  But at age 62 and doing this for 40 years I'm getting really tired of the 7 days, 7 nights, 14-18 hours per day.

My practice is now 25% appointments, 50% portal and 25% drop off.  I hate the portal.  It's so much extra work.  I do not work from my home and I have clients who drop off at midnight or later either thru my mail slot or they know I'll be here.

I live in a higher income area so we get a lot of people with all kinds of investments.  I see the people who do 800 1040's and go no way unless they were simple returns or kids with no kiddie tax.  I also handle a lot of businesses and that helps to kill tax season too.  I also put on my website and appointment scheduler I am no longer accepting new clients.  Helps to cut down on some of the phone calls or else I'd be doing 10,000 returns.  Anyways, good luck and back to work.