Live 1/2, 300 max, winner @ $40 an hour.

What can I expect to be a standard down swing?

If your actual win rate at 1/2 is 40/h, that means it's around 100-200bb/100, which seems impossible to me.

The biggest downswing you should go on is probably around 900 with that win rate.
Though I seriously doubt that's your actual win rate.

A realistic downswing with a decent win rate is probably 10-20 buy-ins.
Really depends on your actual win rate though.
And that's impossible to know in live games since they go too slow.

https://www.primedope.com/poker-variance-calculator/

No solid wr winner is swinging 20bi at live 1/2. Probably somewhere in the realm of 5-10 bi, but also 20bb/hr is not considered a sustainable wr. 10-12bb/hr is already considered very strong.

Primedope is a good resource, and you can see with a wr of something like 30bb/100 you very rarely swing 10+ bi.

20 BI's is very possible if you're only winning for 1-2bb/h
obviously if you're crushing the chance of a 20 BI downswing is insanely low, but still not impossible
doubt OP is crushing though

I reckon there are very very few consistent live winners making just a couple bb per hr. With that said, at a more modest live wr you can see definitely see 15bi swings and maybe the rare 20.

But if we're talking about good+ winrates (which live are like 20bb/100+) those swings don't really exist. Achievable and even decent live winrates are many multiples higher than online so the swings get pretty small if you're solidly winning.

Stacks can get pretty deep live, which might contribute to both higher winrates and larger downswings. It's much harder to lose 20 100 bb buyins as a 70/30 favourite then it is to lose three 700 bb stacks getting it in as a 70% favourite.

This .. and this again.

'How' you win will have a greater influence on swings than most any other factor IMO. If your opponents don't adjust, then the likelihood of a major downswing is much lower .. as long as you aren't just running super hot and flipping 'all the time'.

What's your average pot size? How often are you going to Showdown? How well do you control pot size in flip/marginal spots?

I have seen the most Nittiest of Nits lose 3-4K in one week at 1/2, so even with that style of play 'it can happen'. AA cracked, set over set, the whole gamut of coolers all in a short period of time. Win a BI, get felted an orbit later, start over.

There's going to be speculation on your rate for sure. Players go sessions without seeing AA or hitting a set, much less getting paid when they hold them. That's not to say that you can't win without them, but to be able to manufacture wins at that rate probably needs some help from variance or a really loose Player pool. GL

How much do you lose an hour when you are not winning $40/hr?
I would be shocked if this winrate is for more than 200 hours.
The best poker player in the room I play in does not win $40/hr, not even close.

It would be extremely rare. 98% of nits go home after a 3 bi loss.