Rule on this debate.  

Pilot is 40+
1st class medical. 

EXPIRED on 05/2021

FAA - ATP 

Works a 91 gig only thag doesn't require a  first class any longer.  

Good to fly til 5/31/2021 (expired)

or good til 5/31/2022 ?

what say you ?

It's not just the FAR's that were written to confuse. What are you actually asking?

The FAR's are pretty clear in their chart, 61.23(d), If you hold a 1st class, and you are any age, conducting an operation requiring a Commercial Certificate, then 12th month after the month of the date of examination shown on the medical certificate.

doesn't even make sense.

"Rule on this debate.   

"Pilot is 40+
"1st class medical. 

"EXPIRED on 05/2021

"FAA - ATP 

"Works a 91 gig only thag doesn't require a  first class any longer.  

"Good to fly til 5/31/2021 (expired)

"or good til 5/31/2022 ?"

When was the actual st class physical done?

it doesn't matter who you work for, under what part or what pilot certificate level you hold. the rules are all the same. 

Under the new regulation, third class medicals issued to pilots under age 40 became valid for a maximum of 60 months, up from 36 months. Pilots who are age 40 and older will still renew a third class medical every 24 months.

First class medical certificates are now valid for 12 months for pilots who had not reached age 40 at the time of their medical examinations. Pilots age 40 and over will continue to renew a first class medical every six months.

Under the new regulation, when the first class privileges expire after twelve months, the first class medical lapses to a third class medical. The regulation change does not affect the duration of second class medical certificates, so, for pilots under age 40, the first class and second class medical durations run concurrently for twelve months. 

Wrong. 

class of medical does not change. 

first class is always a first class. 
second class cant turn into a 3rd. 

get back in the books. 

Its all about the privileges you can exercise. So wut.

https://www.youtube.com/watch?v=LIZvYPu4RY8

might be mixing a couple variables.  If the 1st class privilege expired on the date you mention then there are six months left on the commercial privilege, aka pilot flying for hire.  

Simple.

FAA medical regs, you are probably not cut out for a job more complicated than dog walker and that might be a bit much.

Assumptions are all you!

English lessons in ur future.

Vaguely so as to afford the FAA the option of interpreting them any way they want, any time they want.

If you can't figure out the medical regs, you're a complete moron. How is this vague in any way.

so we can mercilessly mock you

You must be dumb! If he is commercial pilot he must have a second class medical that is good for a year! So it will expire 11/30/21

This level of critical thinking bespeaks the helicopter community perfectly, well, not all of it.  There are some really smart people in rotary wing aviation, just not as many, relatively speaking to their respective populations as, say, airline pilots.  

The OP stated the first class expired 5/'21, ergo 6 months left as a second class.

Really?

Millenial action here?

worries, recent ex-mil getting confused 🤔.  Pretty normal these days.

you some of that grammerly. those two sentences are a hot mess bro. like english is your third language hot mess.

We're too hard for you to understand?

the reader shouldn't have to wade through a mess like that for just a simple point. it's wordy. punctuation wrong. vocab weird and pretentious. it's a good example of a middling brain that's trying too hard.

To be preaching on the subject. 

read it out loud to yourself and it might dawn on you how much you sound like a jackass.

Tell us where you are confused. Then point to the place on the doll where they touched you.