Most retirement calculators and most target-date funds run on the same underlying idea: pick an age-based glide path, start heavy in stocks, shift steadily into bonds as retirement approaches, and rebalance annually to keep the mix on schedule. It's a clean rule, and it isn't wrong exactly — but it treats accumulation and drawdown as the same problem solved at different points on one continuous slope. They aren't the same problem. They're solving for opposite things, and the handoff between them is where a portfolio built correctly for one phase can quietly damage itself in the other.
During accumulation, you are a net buyer of assets. Every paycheck, every dividend reinvestment, every 401(k) contribution is new money looking for a price to buy at. In that position, volatility is not primarily a threat — it's the mechanism that makes dollar-cost averaging work at all. A market drop midway through your working years means your existing balance takes a hit on paper, but your ongoing contributions now buy more shares at a lower price, and you have years or decades of future earnings — your human capital — acting as a buffer the portfolio itself doesn't need to provide. This is why the standard advice to stay heavily equity-weighted through most of accumulation holds up: the goal is maximizing expected long-run growth, and the downside of a bad year is repaired by time and continued contributions, not by the asset mix.
Drawdown inverts the relationship entirely. You are now a net seller, withdrawing from a fixed pool with no new contributions coming in to buy the dip. This is where sequence-of-returns risk enters — a concept "The Risk That Doesn't Show Up in the Average" covers in depth — but the short version relevant here is that a market decline in the first few years of retirement forces you to sell a larger share of a shrinking portfolio to fund the same withdrawal, permanently reducing the base that has to recover later. The same volatility that was fuel in accumulation becomes a liability in drawdown, because there's no longer a paycheck refilling the tank. That's the actual justification for holding more stable, lower-volatility assets — usually bonds or cash — heading into retirement: not because bonds outperform, but because they give you something to spend from during a down equity market instead of selling stocks at a loss to cover expenses.
The part a glide-path chart skips over is that the years immediately surrounding your retirement date aren't cleanly "accumulation" or "drawdown" — they're a distinct third phase with its own logic, sometimes called the retirement red zone. Your portfolio is at its largest dollar value right as it's about to face its first real test, and it's also the moment most people execute their biggest rebalancing trades, selling appreciated equities to fund the bond or cash allocation their plan calls for. That timing collision — largest balance, biggest trade, least room for error — is exactly why a market downturn in this window does more damage than an identical downturn ten years earlier or later would.
None of this means a glide path fails, and it's worth being honest about why age-based funds keep working reasonably well for most people despite this collision. A glide path isn't claiming the transition is costless — it's treating the collision as an acceptable cost of simplicity, spread across millions of investors with different retirement dates, different spending needs, and different cash cushions. For someone with a low withdrawal rate relative to portfolio size, a shorter or more flexible retirement horizon, or a healthy cash buffer outside the plan, the red-zone damage is real but survivable. Where it actually bites is narrower and more specific: someone retiring into a tight sequence-of-returns window with most of their wealth concentrated in a single taxable brokerage account, executing one large rebalancing trade in the same year the market turns down.
That's also where the tax mechanics stop being an afterthought. If the rebalancing trade happens inside a 401(k) or IRA, selling stock to buy bonds triggers nothing — no tax event, because gains inside tax-advantaged accounts aren't realized until withdrawal. But the same trade executed in a taxable brokerage account realizes a capital gain the moment you sell, typically at long-term capital gains rates since these are usually long-held positions. That gain adds directly to your adjusted gross income for the year, and for anyone retiring before 65 and buying health coverage on the ACA marketplace, that's not a minor detail. Unsubsidized ACA premiums for a 55-year-old were commonly running well over $1,000 monthly, approaching $2,000 in high-cost states, as of early 2026, and the subsidy that keeps that number lower phases out as income rises — so a large, one-time realized gain from a red-zone rebalancing trade can push a household past the income line where they lose thousands of dollars in premium assistance for that year, on top of the capital gains tax itself. The mechanism causing the damage isn't the market downturn alone; it's the downturn colliding with a discretionary tax event the investor chose to schedule in the same year.
None of this changes what to do during accumulation — stay equity-heavy, keep contributing, let volatility work in your favor. It changes what to check in the years just before and after retirement. If you're five years out and most of your portfolio's growth sits in a taxable account, the size and timing of your rebalancing trade matters more than your target-date fund's glide path assumes: spreading that trade across several years, harvesting losses to offset gains, or routing new contributions into bonds instead of selling stocks to get there can defuse the tax and subsidy collision before it happens. The question worth asking isn't whether your glide path is wrong. It's whether the single biggest trade you're about to make is one your plan scheduled for convenience, or one you chose deliberately with the tax and health-insurance consequences already priced in.