According to this post on The Occupational Adventure:
Looking for happiness through financial success? Wondering what is the magic number that equals satisfaction? It's $40,000 a year.
In fact, the rule is well established in research: The first $40,000 makes a big difference in one's level of happiness. After that, the impact is much smaller. The difference between someone making $40,000 and someone making $15,000 is far greater than the difference between $100,000 and $1 million.
If you think about it, $40,000 vs. a lower salary makes perfect sense. When I came out of college I was making $40K per year. I was able to afford a car payment, an apartment payment with utilities and cable, and still have some money in my pocket to go out to eat and go to bars. I can't say that I was saving an extraordinary amount of money on a monthly basis (I think I was contributing 1 0r 2% to my 401K), but I had shelter, food, water, and wheels: the necessities of life.