7 Common Retirement Planning Mistakes
Most retirement shortfalls don't come from bad luck in the market. They come from small assumptions made early on that quietly compound into a much bigger gap. Here are the ones we see most often.
1. Using current expenses without thinking about how they'll change
People often plug in today's spending and assume it stays flat. In practice, spending usually shifts: housing costs may drop if a mortgage is paid off, but healthcare costs typically rise significantly later in retirement. Revisit your expense estimate every few years rather than setting it once and forgetting it.
2. Ignoring taxes on withdrawals
A retirement account balance is not the same as spendable money. Depending on the country and account type, withdrawals may be taxed as income, and this can meaningfully reduce what's actually available to spend. Build in a buffer if your accounts are tax-deferred rather than tax-free.
3. Picking a withdrawal rate without considering retirement length
The 4% rule was built around a 30-year retirement. Retiring at 45 instead of 65 can mean planning for 50+ years, which usually calls for a lower, more conservative withdrawal rate.
4. Forgetting that "already invested" money is still growing
Some people only think about how much more they need to save, without accounting for the fact that their existing investments keep compounding in the background. This is covered in more detail in our piece on compound interest.
5. Not planning for one large, irregular expense
Averages hide lumps. A new roof, a medical procedure, or supporting a family member can all show up as one large expense in a single year. A cushion above your calculated number, rather than an exact target, tends to hold up better in the real world.
6. Reacting emotionally to market downturns
Selling investments after a market drop locks in the loss and removes the chance to recover when the market rebounds. Historical retirement research generally assumes the investor stays invested through downturns — the math falls apart if that assumption is broken.
7. Never revisiting the plan
A retirement number calculated once at age 30 is a starting estimate, not a fixed target. Income, expenses, family situation, and markets all change. Recalculating every year or two, adjusting the inputs as life changes, keeps the plan useful instead of stale.
What each mistake can cost, roughly
| Mistake | Rough impact |
|---|---|
| Ignoring a ~20% tax on withdrawals | Effectively need ~25% more saved to cover the same spending |
| Sizing around total spending, not essential spending | Target inflated by however much discretionary spending was included — often 20-30% |
| Not lowering the withdrawal rate for early retirement | Underfunding risk that often only surfaces 15-20 years in, when it's hard to fix |
| Never recalculating after a raise or life change | Plan drifts silently out of date, often discovered only near the actual retirement date |
Figures are illustrative, not precise — actual impact depends heavily on individual circumstances.
Frequently asked questions
Once a year is a reasonable default, or any time something significant changes — a new job, a move, a new dependent, or a shift in your expected retirement age.
There's no universal answer, but many planners treat the calculator's output as a floor, not a ceiling, adding 10-20% if expenses are hard to predict or you have limited flexibility to cut spending in a bad year.
If you expect guaranteed income from a pension or government program, you can reduce your monthly expense figure by that amount before entering it into the calculator, since that income will cover part of your costs regardless of your portfolio.