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What is the best use of “spare” money?
With 40% of your take-home available, you have a golden opportunity here. Actually two, and the second builds out easily from the first.  Golden Opportunity # 1: Layoff Immunity Ok, not really immunity. Most people don't think of themselves getting laid off, and don't prepare. Of course it may not happen to you, but it can. It's happened to me twice. The layoff itself is an emotional burden (getting rejected is hard), but then you're suddenly faced with a gut-wrenching, "how am I gonna pay the rent????" If you have no savings, it's terrifying. Put yourself in that spot. Imagine that tomorrow, you're out of a job. For how many months could you pay your expenses with the money you have? Three months? One? Not even that?  How about shooting for 12 months? It's really, really comforting to be able to say: "I don't have to worry about it for a year". 12 months saved up gives you emotional and financial stability, and it gives you options -- you don't have to take the first job that comes along.  Now, saving 12 months of expenses is huge. But, you're in the wonderful spot where you can save 40% of your income. It would only take 2.5 years to save up a year's worth of income! But, actually, it's better than that. Because your 12-month Layoff Immunity fund doesn't have to include the amount for retirement, or taxes, or that 40% we're talking about. Your expenses are less than 60% of take-home -- you'd only need 12 months of that. So, you could have a fully funded 12-Month Layoff Immunity Fund only in a year and a half!  Golden Opportunity #2: Freedom Fund Do you like your Job? Would you still do it, if you didn't need the money? If so, great. But if not, why not get yourself into a position where you don't need it? That is, build up enough money from saving and investing to where you can pay your expenses - forever - from your investments. The number to keep in mind is 25. Figure out your annual expenses, and multiply it by 25. That's the amount you'd need to never need a job again. (That works out to a 4% withdrawal rate, adjusting for inflation every year, with a low risk of running out of money. It's a rule of thumb, but smart people doing a lot of math worked it out.) Here you keep saving and investing that 40% in solid mutual funds in a regular, taxable account. Between your savings and the compounding returns off the investments, you could easily have a fully funded "Freedom Fund" by the time you're 50. In fact, by 45 isn't unreasonable.  It could be even better. If you live in that high-rent area because of the job, and wouldn't mind living were the rents are lower once you quit, your target amount would be lower. Between that, working dedicatedly toward this goal, and maybe a little luck, you might even be able to do this by age 40.  Final Thoughts There are other things you could put that money toward, like a house, of course. The key take-away here, is to save it, and invest it.  You're in a unique position of being able to do that with 40% of your income. That's fabulous! But don't think it's the norm. Most people can't save that much, and, once you lose the ability to save that much, it's very difficult to get it back. Expenses creep in, lifestyle "wants" become "needs", and so on. If you get into the habit of spending it, it's very difficult to shrink your lifestyle back down - down to what right now you're perfectly comfortable with. So, spend some time figuring out what you want out of life -- and in the mean time, sock that 40% away.