Many financial advisors say you’ll need some fixed percent of your previous income in retirement—often 80% is considered “reasonable.” But that’s nonsense. What it costs you to live in retirement, or before, is not a function of how much you make! There are millionaires who live like college students, and college students who live like millionaires—for a while anyway, on credit. Where are you on the lifestyle spectrum? To get serious about retirement planning, you’ve got to have an accurate picture of your monthly living expenses. You need to know your bare minimum or fixed expenses, your average or normal expenses, and your ideal expenses—allowing for some luxuries. Spending is a personal area, so everyone’s pattern will be different. But on average the first phase of retirement is when you’re likely to spend the most, since you’re finally free to travel, dine out and enjoy other leisure activities. Among older Americans, average annual expenditures peaked at about $61,000 for those in the 45-54 year age range, according to the latest data from the Consumer Expenditures Survey. By ages 55-64, spending dipped to $56,000, and down again to $46,000 between ages 65 to 74. At 75 years and older, average spending was only $34,000, though health care expenses may spike up for many. We are in our mid-50’s and live a modest but comfortable lifestyle, which currently costs us about $4,500 a month, in addition to housing. We rent a smaller, two-bedroom house (about $1,500 monthly), and share a single gas-efficient car ($370 a month, including gas, insurance and repairs). But we eat well, own some nice things, and have plenty of fun—mostly free or cheap outdoor activities. And our living expenses run about 25% above the national average for our age. This past year we moved to our ideal retirement location. So we’ve had to spend a bit more than usual due to the relocation. But these have generally been one-time home or personal expenses—not recurring expenses that would inflate our lifestyle forever more. Health care costs remain a concern, since we are too young for Medicare. Fortunately, I was able to get coverage through my wife’s retirement health plan, thanks to her former career as a public school teacher; we pay $1,100 a month on average for premiums, co-pays, deductibles and the like. That’s one of our larger expenses, but it is manageable, for now. (For more on our spending in early retirement, see my blog here.) If you’re willing to live in a cheaper area, buy used, and eat simpler, you can probably live on much less than we do. On the other hand, if manicured retirement communities, luxury vehicles, and international travel are your idea of retirement living, you could need quite a bit more. In most surveys of consumer expenses, the biggest items are housing and transportation. So, if you want to optimize your retirement lifestyle, start with your home and vehicle. Without a complete understanding of how much it costs you to live, your retirement planning can’t get off the ground. The best way to determine your expenses is to actually keep track of them for at least a year, as you approach retirement. You can record expenses using dedicated tools like Quicken on the desktop or Mint on the web, or you can use an electronic spreadsheet or paper journal. As an engineer, tracking expenses was second nature to me. But what if you aren’t the detail-oriented type? You could estimate your expenses based on those government averages above, but in the long run you’ll need more accuracy to be confident about your own situation. One approach is to sit down with your checking and credit card statements, and use them to estimate a monthly or annual amount for each important budget category. You can start with this short list: housing, transportation, food, health care, entertainment, and personal expenses. Just don’t forget those less-frequent items such as home and auto repairs, vacations, and property taxes! Your retirement savings “number” gets a lot of press. But even more important than that is your expense number. Understanding your expenses is a critical stepping stone to building wealth and retiring comfortably. If you still don’t know where your money goes, why not get started today? Darrow Kirkpatrick is a software engineer and author who lived frugally, invested successfully, and retired in 2011 at age 50. He writes regularly about saving, investing and retiring on his blog CanIRetireYet.com. This column appears monthly.