A good benchmark is apartment rentals. Your average landlord will require that your annual income be 40 times the monthly rent. For instance, if you want to live in a $2,000/month studio apartment in Manhattan (which is on the low end of the range for apartments in Manhattan, but not uncommonly so), you’ll need $80,000 a year.
That’s not a bad basis for your calculations. Figure on 30 percent going to taxes. So your monthly take home will be around $4,600. $2,000 for rent. Another $500 for expenses like cell phone, a subway pass, utilities, cable/Internet, maybe a gym membership if you skimp on the other expenses. Now you’re left with $2100 to play with. Is that enough for fun and comfortable? Depends on what you do for fun.
For instance, people eat out a LOT in NYC. Esp. if you live in Manhattan, because unless you live in a palatial apartment (in which case, you wouldn’t have needed to ask this question), your kitchen is miniscule, and your apartment is so small that you can’t cook anything that isn’t instant/microwaveable without stinking up your home for days. Plus groceries are so expensive that you’d hardly save much money cooking anyway. So let’s assume $20 a day during the week for takeout (lunch and dinner), and $100 a day on weekends (you’ll go to a nicer place with your friends to hang out). That’s $300 a week on food. You have $900 left for the month, or $225 per week of spare cash. While it’s possible to drink cheaply in NYC, it’s also absurdly easy to blow through $225 in a weekend of NYC nightlife, even if you’re not going to the velvet-rope clubs. And don’t forget that part of this $225 needs to be put away to buy new clothes occasionally, or for savings.
Now, of course, plenty of people live in NYC and make less. You can do that if you get (or have) roommates, if you live in the outer boroughs (or even New Jersey), or both. You can do that if your idea of fun doesn’t necessarily include Broadway plays, clubs in the Meatpacking district, dining at places you read about on Chowhound/Eater/New York magazine/etc, or going to see well-known bands. If you don’t need to shop in Soho or Manhattan in general or wear a suit and tie (or the female equivalent) for work. If you’re content to subsist on food sold by street carts or at divey Chinatown spots (much of which, it must be said, is quite tasty and delicious.)
I’ve read news stories about some very creative ways people make do with less money. For instance, for housing, I’ve read about people who cram four to a room, building bunkbeds and sleeping in shifts, etc. If you work in fashion, entertainment or PR, many people feed themselves through food at work functions (receptions and such) — gorging themselves, surreptitiously sneaking extra food home, etc. — and eating instant ramen whenever the functions aren’t taking place.