I'm in a somewhat similar boat; probably a bit less take home, in the consulting/finance area, higher base.

Based on this MMM post, if you can get by on 4% of the total pile of money you have invested in the market today, you can retire today. Assume 5% real returns (20% LT capital gains), and you never touch principal. Right now, after all my savings I have ~$6,000 take-home, so to replace that I need $72,000 in income from investments in order to have the same standard of living in retirement as I have today, which if it's after tax, we have an after tax required rate of return (matching the cash flows) of 4%, so $72,000 / 4% = $1.8 million. If I had $1.8 million (after tax - but we can ignore that nuance for now) in the bank right now, I could quit my job and never work another day in my life if I didn't want to, or do something more noble / fulfilling, pursue another career to add to savings, whatever. It is my goal to get to that level of savings as soon as I can, and therefore I save a percentage that I think is reasonable: somewhere between 30% and 40% of my income. I expect my wages to go up, costs to stay constant (mortgage, so fixed housing cost), so I can increase my savings both nominally and as a percentage of income.

For me, I think that I'm being conservative. I'm assuming the same rate of return as MMM (5% real returns over my life time) and I consider social security my "safety margin" - extra income that could make up any shortfalls in my savings. My income is over the social security tax cap, meaning that if this earnings level keeps up for me into retirement, social security will be an additional ~$4k / mo in today's dollars. That's a pretty big safety net, even assuming it gets haircut by 30% or so in the future.

Now as far as saving: I don't do it by numbers in a concrete way, but a bit more emotional. My math is essentially a combination of 1) how much more can I save as my income grows, 2) how much have my investments grown in excess of my planned rate of return, and therefore, how far ahead of schedule am I?

In my current state, I'm in my late 20s, net worth around $350k, of which about $150k is home equity (mostly appreciation - not a big purchase). If we assume that the whole pile gets 5% real returns from now until I retire, then that implies (1,800,000 / 350,000) ^ (1/34) = 4.93%, or, in other words, if I don't contribute another dime to my retirement, then as long as I live off of my earned income (i.e. not off the pile of money I saved up), then if I work for another 34 years, I will be able to retire assuming 5% real rate of return. I could spend my fixed expenses (shelter, food, etc.) of $3k / mo, and spend the other $3k / mo traveling, and have it not affect my retirement one damn bit, if I'm okay working for another 34 years. This ignores, for the time being, that at that time I would be approaching social security age and would only have another 5 ish years until I could withdraw the full social security benefit at age 70 - which is my safety margin.

Expressed differently - I don't need to save anymore, if I really don't want to, and I want to spend money instead.

My personal choice, is that I want to keep saving until I'm more certain. This is for a variety of reasons that may be outside the scope of this post. I'm pessimistic about the future of the U.S. labor market, and don't know how much longer I will be able to put away this much money. I think it's likely it'll be for a while, and that my income will grow significantly before it drops off - but it's a fear. There's also a chance my company will have layoffs (not likely again; we had an amazing year this year and are expanding rapidly); or that I will be laid off (unlikely based on my performance thus far); or that I will quit because I go crazy (more likely than the above scenarios) and do something much lower paying; or that I get hit by a car on my commute into work and can no longer do my job; myriad fears that people need to self insure against. My safety net is on the smaller side (from a social support network perspective), so I err on the side of caution.

However - all the above being said - I'm planning a trip to south america this summer. I don't mind putting a couple thousand towards something like that - one month of my savings makes up for it. I should cut back on my eating out and going to bars, probably ~$1k / mo total, but I don't feel much pressure to do so at this point. I have fun going out with friends, buy gifts here or there, donate some money. That's all from my "after savings" earnings on base salary. Bonus is maybe 10-20% each year, and that goes right into my savings too. I usually get a tax refund thanks to interest deduction and state income and property taxes paid, and that goes right back into after tax savings.

At the end of the day, it's all about understanding what your income distribution looks like into the future, and whether or not you're on track to saving enough to retire on terms you're comfortable with, and that you have a margin of error built in. Basically, at this point, if I go on a vacation it might mean that I'll work for 23 more years before I can fully retire, rather than for 22.9 years. Not that big of a difference, not that big of an issue. If I switch careers, maybe I'll adjust my spending down and work a bit longer, say 30 years. The more you save up early, the more choices you have about what you can do - for me it's all about keeping in mind that my goal is to get to a level where I can retire whenever I want based solely on my savings.