I realized something recently. I'm not sure why it took so long. It seems simple and obvious now. You've probably already realized this, but if not, here's a nugget of truth:

You Can't Spend More Than Half Your Income

I'm not talking about net income. Physician on FIRE challenges those seeking FIRE to “live on half.” That's not what we're talking about here. I'm talking about the answer to this question:

How much of my gross income can I spend each year and expect to be able to sustain my standard of living throughout my life?

It turns out the answer to that, at least as a general rule of thumb for a high-income professional, is “about half”. Why is that you ask? Because the other half has to go to taxes and savings. It has to. The taxes aren't optional and they're going to be fairly high for most of us during our peak earnings years. The retirement savings is optional, I suppose, but not if you wish to actually avoid eating Alpo.

Take a look at the math.

Taxes Eat Up Lots of Your Gross Income

First, let's think about taxes for a bit. When I was making the average physician income, my effective tax rate was in the teens. But it turns out I was a fairly unusual case. Most docs pay an effective rate in the 20-30% range, some a little more, some a little less. So if you subtract out 30% of your gross income for taxes, that leaves you 70%.

Safe Savings Rate

Next, let's look at what kind of a savings rate is needed to provide a reasonable retirement. Long term readers know I generally recommend docs use a 20% saving rate. Will they be okay with 15%? Probably. But 5-10% just isn't going to cut it. Let's demonstrate why it needs to be higher than that with a simple future value calculation.

Let's take a doc making $200K who starts saving for retirement at 35 and hopes to retire at 60. She earns 5% real on her investments and saves 20% a year? How much will she have at age 60 and how much of her pre-retirement income will that replace? Plug this into your friendly spreadsheet:

=FV(5%,25,-40000) = $1,909,084

Live On Half your income

Spending more than half your income is riskier than rappelling

Multiply that by about 4% and it gives you an income from your portfolio of about $76K real per year. That's about 38% of your pre-retirement income, which is smack dab in the middle of that 25-50% range that a typical doctor needs in addition to Social Security to maintain her standard of living in retirement, assuming the kids are launched and the house is paid off.

So subtract out another 20% from that 70% you had after taxes and that gets you to 50%. That's what you can spend if you hope to avoid ever having to decrease your standard of living. Said another way, if you spend more than that regularly, you're going to have a lower standard of living in retirement.

Higher Earners Have It Worse

The percentage gets even worse if you make and spend more than the typical doctor. That's because the tax code is progressive. It is progressive during your earnings year and it is still progressive in your retirement years. In addition, the more you make and spend the lower your relative contribution from Social Security will be.

Consider another example:

How much peak earnings income does it take to create a sustainable $400K a year after-tax spending level? A lot more than you might imagine. Let's start at the end and work back to the beginning.

In order to spend $400K a year in retirement, you need about 25 times that as a nest egg, or $10 Million. At that sort of spending level, Social Security can almost be ignored. But wait, you need $400K in after-tax money. At that sort of tax bracket, you're probably looking at an effective tax rate of at least 24%, perhaps 32% even in retirement. So we're really talking about perhaps a $13 Million nest egg.

How much do you need to put away each year at 5% real to have $13 Million after a 25-year career?

=PMT(5%,25,0,13000000) = $272,381.

So add that on to your $400K. Now we're up to $672K you need to earn in order to sustain a $400K spending level. But wait, we haven't considered the taxes as you're earning the money. At that sort of income level, perhaps 35% of what you earn is going to be going to the tax man. That means you need a gross income of $1.04M during your career to sustain a $400K spending level throughout your life. That's 38%, significantly less than the 50% for an “average doc”.

Sobering isn't it. I've written before that you can never grow all the way into your income. If you're smart, you'll never grow into more than half of it and you'll begin your career living like a resident on much less than that. And we're not even talking about retiring early here. This is just regular old retirement.

What do you think? Did you imagine that you would only be able to spend 40-50% of your gross income when you applied to med school? How much of your gross income do you spend after taxes and savings? Do you think that is too little or too much? Comment below!