SuttaCentral
Lay person, according to the suttas, can become an Arahant at the moment of death. Non-ordained Bahiya did become an Arahant but died before ordaining. Maybe this is one of the reasons for “lay person has to ordain within 7 days or die” teaching. Certainly a lay person who becomes an arahant will not be able to function in the world (and thus could at least starve to death), unless becomes monastic ASAP.
In the suttas there are also many stories of lay anagamis.
What would be the hindrance for a layman not to become an arahant ?
Say it’s not an internal reason, for example it’s not that he doesn’t want to ordain because he is too much attached to his wife and relatives.
But it’s an external reason, for example he has debts and can’t ordain as a bhikkhu.
So, what is or what would be the reason in that case that he can’t become a lay arahant ?
They can be lay arahant, but classical Theravada just say they cannot live for too long.
You mean to ask why they cannot live for too long?
The life of a lay person has not enough virtue/precepts to contain the pure mind of an arahant.
Arahants do not long for death or life, without desire, they don’t work (for money), they might not eat. Non returners it seems already don’t use money.
Maybe when ordained, even as a sāmaṇera (as there were kid arahants), out of respect for the Buddha, dhamma and saṅgha, they go for alms arounds and eat and thus continue to survive.
I had heard that one way to verify authentic Bhikkhuni ordination is to see if an arahant bhikkhuni would live long. I think perhaps people forgot that there were sāmaṇera arahants. So it could be in general that a recluse lifestyle which is more of the factor to increase lifespan of lay arahant.
Certainly, it’s not too hard for a dedicated lay people to set up conditions so that they can live with 8 precepts or more. Anagārika/Postulants (similar to samanera, but in white robes) in SBS are not strictly speaking a part of the 5 saṅgha (Bhikkhu, Bhikkhuni, Sāmaṇera, sikkhamāna, sāmaṇerī), but could be enough. And many other semi monastic styles which cropped up in modern times. Including Sayalays or Mea Chees.
Off topic, but interestingly, if lay arahant can live longer just by current action of ordaining, then this would have implication for their total old kamma to be used up.
Classical Theravada says infinite old kamma, cannot finish used up by arahant in last life, so no body or mind in parinibbāna means the rest of the infinite old kamma got defunct.
EBT have this AN10.217 which says no ending of suffering without ending kamma. AN 10.217 Paṭhamasañcetanikasutta
So let’s say a lay person got arahanthood is due to die in 7 days, their kamma would accelerate fast to ripen within 7 days. But got ordained within 7 days, suddenly got new kammas to support living more than 7 days as a result of actions done while an arahant? Or perhaps it’s just changing conditions made by arahant, which causes the remaining old kamma to be slower in ripening for longer lifespan rather than to jam-pack it all within a few days.
Or like Bhante Aggacitta would put it that arahant can still make kamma, like eating causes them to live longer. Just that the kamma doesn’t produce results for next life, only this life.
from my recollection, the buddha specifically leaves out lay people from his description of arahants, but he states lay people can be stream enterers, once returners and non returners. i unfortunately can’t find the sutta right now, but it’s quite striking to read - it stands out that he omits male and female lay practitioners from his description of arahants but includes them in the other three stages of enlightenment.
i interpret this to be consistent with the ordain or die idea suggest by nagasena. if there isn’t the kamma for a person to become a monastic, then i imagine on arahantship, they have nowhere to go. they are no longer a layperson, and they are not an ordained monastic.
if i find the sutta reference i will update my comment (or if anyone else knows it please reply to me!!)
edit: this is one such reference but not the one i was thinking of:
When this was said, the Wanderer Vacchagotta asked: “Master Gotama, is there any householder who, without abandoning the fetters of householdership, makes an end of suffering on the dissolution of the body, after death?”
“There is no householder who, without abandoning the fetters of householdership, makes an end of suffering on the dissolution of the body, after death.”
I stand corrected. It’s also EBT’s stance.
My guess it’s kind of similar to paccekabuddhas. It would be exceedingly difficult, and certainly number of monastic arahats would outnumber lay arahats on a scale of %99 or something like that.
But they might just have basic familial obligations, taking care of the sick and such, or having such a peaceful virtuous life that even the monastic requirements and life is a burden on them. Why bother memorising entire vinaya and keeping up with to-the-letter requirements of a tradition? There’s no fault to find in them, they’re just immersed, living on the food given by elders and locals (I’ve seen such “mad” wise people in some villages), sustaining on kindness. There are sufi mystics that really fit the bill of arahats, that live off alms or by their family’s kindness.
So they might’ve left the fetters of householdship in their heart, but they’re not just monastics either.
Please note, I’m not saying “They are arahats for sure” but I’m trying to answer “How can lay people be arahats?” and answering from that inquiry. That’s my understanding of it.
I agree, it does sound pretty much like that.
But the Pāḷi is amataṁ sacchikatvā:“having experienced the deathless [state]” (i.e. Nibbāna) which sounds much more like Stream Entry to me 
But what’s the difference between the two? Both “the deathless state” and “freedom from death” translate the same Pali term, amata.
The entire phrase reads amataddaso amataṁ sacchikatvā iriyatī—and “seeing” that freedom from death, or deathless state, and “living having realized” it seem to be two different things to me.
thank you bhante - that’s exactly the one i was looking for.
i hope you are keeping well.
Yeah, or why list them separately? I hear you.
I read that as just highlighting how the experience changes you. You can’t live the same way after having experienced the deathless as you did before.
I don’t know. I always thought the first one refers to stream entry and the second to perfection. That is (one of the reasons) why this passage seems so puzzling.
BB is currently holding by 6.30ish in his Saturday class.
He will possibly get there in a few weeks.
I now found that at least two of the people listed in this sutta appear elsewhere as gods after their death, Anāthapiṇḍika in SN2.20 and MN143, and Hatthaka of Āḷavī in AN3.127.
So it is clear that they are not arahants.
Of others it is said that they have become non-returners, for example the householder Citta in SN42.9 and Ugga of Vesālī in AN8.21, and probably more.
And I also found this old thread, so perhaps the two can be merged. @moderators?
So in any case, thank you all for your contributions, this helped me to get the point clearer for me. 
Is it true the story of king Śuddhodana attained arhat at the end of his life as a lay person ?
Yes, that’s how the story goes. Occasionally lay disciples became arahants on their deathbed, but never is there talk that they live with that attainment. Don’t ask me why, though …
Is it so far fetched that some of us doesn’t aim for what they have been told, even by skilled and educated monastics?
The context could be qualified doubt that even what we take to be early scriptures doesn’t have to be correct and therefore true. I have great respect for the rogue or more punky style like the Thai Forest traditions origins, and the diversity in style and capability to include their own programming in western culture.
Ajahn Chah," If you have time to breathe, you have time for meditation."
Thats true for me, and where it ends, is obvious
This isn’t EBT, but a hilarious (in my opinion 
) sutra in Mahayana that depicts a lay disciple teaching extremely venerated Ariya beings and monastics in a way that leaves them reluctant to endure his scrutiny.
As stated in the introduction:
The Buddha asks his disciple and bodhisattva disciples to call on Vimalakīrti, but each of them relates previous encounters that have rendered them reluctant to face his penetrating scrutiny of their attitudes and activities.
…
Its masterful narrative structure, dramatic and sometimes humorous dialogue, and highly evolved presentation of teachings have made this sūtra one of the favorites of Mahāyāna literature.
This is considered authentic Buddhadharma in many extent Mahayana traditions so it could be that monastics in those traditions might not have the same understanding of the limitations of lay disciples. I dare say this sutra might act as a condition for relieving the conceit of monastics towards lay disciples
Hi Sabbamitta Silashin,
I’ve merged both threads now.
Regards,
suaimhneas (on behalf of the moderators)
However the story doesnt found in the suttas but commentary . Sutta mentioned he only attained sotapanna .