Target date funds are a sound default for someone building a balance and a blunt instrument for someone about to draw income from it. They are personalized on exactly one variable — your birth year — and that becomes a real limitation as the balance grows and the plan gets specific.
Most workplace plans default new enrollees into a target date fund, and for that purpose they work well. They are diversified, automatically rebalanced, and vastly better than an unallocated cash balance or a single-fund guess.
The trouble starts when a default designed for a 25-year-old with $4,000 is still running a 58-year-old's $900,000 account without anyone revisiting it.
It is personalized on one input
A target date fund's glide path is set by an assumed retirement year derived from your date of birth. It knows nothing about your other assets, your pension, your spouse's accounts, your risk tolerance, your tax situation, or when you actually intend to stop working.
Two people with the same birth year — one retiring at 55 with a pension, one working to 70 with no other savings — receive an identical allocation. There is no version of that which is right for both.
Limited underlying choice
A target date fund holds the fund family's own component funds. Whatever that family does well and whatever it does poorly, you own both, and you have no ability to substitute a better option for a weak sleeve.
You also inherit the fund family's view on questions like international allocation and bond duration — reasonable positions, but positions, and you are holding them by default rather than by decision.
The income stage is where it strains most
This is the significant one. A target date fund is a single blended pool. When you need to withdraw, you sell a slice of the whole thing — including the equity portion — regardless of what the market did last quarter.
That is the opposite of a bucket approach, where near-term spending is deliberately held in stable assets so that a downturn is funded from the reserve rather than by selling depressed holdings. You cannot implement that inside a single all-in-one fund, because there is nothing to draw from selectively.
Tax location and coordination
Once a household holds assets across a 401(k), an IRA, a Roth, and a taxable account, which asset sits in which account starts to matter. Holding the same blended fund everywhere forfeits that.
The related problem is coordination. If both spouses hold target date funds in separate plans alongside a taxable portfolio, nobody is managing the household allocation — three separate autopilots are, and they cannot see each other.
None of this makes target date funds a bad product. It makes them a default, and defaults deserve review once the balance is large enough and the retirement date close enough for the details to matter. If you are within a decade of drawing income and your plan is still on autopilot, that is the moment to look at it deliberately.