Dear Liz: I keep reading about how much money one should have saved at various ages to comfortably retire. These are usually a multiple of your annual salary. Do these projected amounts factor in whether you are single or married with a single income? Or if you still have a mortgage? What about having to take a lower-paying job in future years because of downsizing? Is Social Security included? It’s tough to know what these suggested amounts assume to know, given that each person’s situation is different.

Answer: Exactly. So it’s smart to do a little digging.

Fidelity Investments, for example, has come up with some salary-based rules that suggest you have an amount equal to:

One time your salary by age 30

Three times your salary by age 40

Six times your salary by age 50

Eight times your salary by age 60 and

10 times your salary by age 67.

Fidelity assumes you’ll want your standard of living to continue basically unchanged in retirement. Its rules are based on a number of factors, including a 1.5% real wage growth throughout one’s working life, a 15% savings rate starting at age 25, claiming retirement and Social Security at age 67 and a portfolio invested at least 50% in stocks that replaces 45% of your individual income in retirement. Fidelity used multiple market simulations “to support a 90% confidence level of success.”

Few people’s lives will follow an idealized trajectory. For example, many people who enter their 50s with full-time jobs will lose them, and only 1 in 10 will find a new one that earns as much, according to a study by ProPublica and the Urban Institute. You can’t know for sure how long you’ll live, what investment returns you’ll get, whether you’ll need long-term care (although that’s likely) or even what your fixed expenses will be, at least until you’re relatively close to retirement.

People also will have vastly different needs and interests in retirement. A thrifty homebody will probably need less than a globe-trotting spender. Working at least part time in retirement also can shift the math in your favor because you’ll need to draw less from your retirement funds.

What we do know is that people who save a lot tend to have more options as they age. And once you reach your 50s, you’d be smart to consult a fee-only financial planner who can give you a second opinion on your retirement plans to ensure you’re on track.