This sounds like math done by someone who has never earned an income as low as $40k.
Some slightly more realistic numbers (rounding to nearest hundred):
Income - $40,000
Federal - $3100
State (variable, this is for CA) - $1000
Social security - $2500
Medicare - $600
Disability (again, CA) - $500
Total tax - $6700 in CA, maybe $5200 in a lower tax state
$13k annually for rent (in CA, that’s very cheap).
How much for health insurance? Probably $1k-$2k.
How much for transportation? That’s car payment/repairs, insurance, and gas in most places. This eats up a lot of disposable income for people.
Cable tv, cell phone, etc. also adds up quickly.
Oh, you better not have student loans. That will eat up more of your disposable income.
I have given some budgeting tips to people who make ~$50k working in California. At best, they can contribute the 5% for matching, but it’s tough. Things like increased gas prices, unexpected car repairs, medical issues, etc. are a huge fear and a major concern.
Sure, $40k is very livable in provincial parts of the US, but there are many many people who do not live in those areas but make that income.
Just trying to keep it real…