Below is my post-tax income normalized to my first full year's earnings in the workforce, and SPY growth normalized to the same year. I've invested time in my career and grown my post-tax income ~2.5x in the past 12 years, but the market has handily outpaced me. This would suggest that my most valuable passive investing days from a wealth creation perspective are already long behind me:
However, if I pull out my (simplified but still pretty close--take my growing expenses as a present consumption preference for my family) variable and fixed costs, I really didn't have a lot left over to invest early on in the first place. Even though my post-tax income growth was only 2.5x over the last 12 years, I actually had about an 8x growth in what I was able to put into the market vs. when I started:
As a long-term investor (until I start de-risking) I really only care about the price of the S&P500 30 years from now and how many shares of it I own. So I can measure the total 'wealth' I'm gaining every year by just counting the number of shares I purchase (for simplicity, let's set aside the tax advantages that come from % in retirement accounts, more recent shares having a higher cost basis, etc.). Dividing the shaded area above by the growth in SPY share price yields the number of shares bought per year (normalized again), which is the chart below:
From a future wealth creation perspective, what I'm investing annually today is worth twice as much as what I invested in my first few years despite over a decade of market growth in the latter.
Before I started looking at this, I'd always implicitly assumed that "start saving early" and "compounding compounds" were unassailable mantras, but in actuality those first 5 years only produced about a quarter of my current invested wealth, property aside (2016 was a new home at the max of my debt-servicing capacity). 20 years from now it'll be at most ~10% even if I took my foot off the gas tomorrow from a career POV. 10% of everything is a lot, but it's not "you lost before you began" levels, either. Below is that long term view with only inflationary income raises of about 1.85% post-tax for the next 20 years (and SPY growing at 9%):
When I first looked at this years ago, I had to double-check the math. Even after investing for three decades, a full 30% of my retirement fund is the same dollars I put into the market (blue). That is an enormous amount of money. That's not to say investing doesn't matter--that 250% return from the market is the lion's share, and the equivalent of 60 years additional work--but comparatively, the market will have increased by over 2,100% during the same 31 year timeframe. If I think about my daughter, aside from helping with fixed costs, if I can just get her set up with a fraction of money post-college and lock it away, she will enter her own later years with an entire other career's worth of accumulated wealth for free.