How Much Does a 0.5% Difference in Withdrawal Rate Matter Over 40 Years?

The decimal point that doesn't look like much

If you're trying to decide between a 3.5% and a 4.0% safe withdrawal rate, the headline difference is half a percentage point. On £40,000 of annual spending, that's the difference between drawing 3.5% from £1.14m or 4% from £1m. The annual amount is identical. The portfolio sizes look broadly similar.

Compound it over 40 years and the story changes completely.

What 0.5% does to the FIRE number

The arithmetic is direct:

• 4% rule: FIRE number = annual expenses × 25
• 3.5% rule: FIRE number = annual expenses × 28.6 (which is 14.4% more)

For a £40,000/year target:

• 4%: £1,000,000
• 3.5%: £1,142,857

The £142,857 gap represents extra accumulation. For a saver putting away £40,000/year at a 5% real return, that's roughly 1.8 years of additional working time.

The trade-off is starkly asymmetric: 1.8 extra years of work in exchange for a substantially safer retirement that's 14% more bulletproof against historical sequences. Most planners take the trade.

What 0.5% does to terminal portfolio outcomes

That's the easy side of the math. The compounding side is more dramatic.

Run a 40-year retirement at both rates with a £1,000,000 starting portfolio against the Shiller record:

• At 4% withdrawal:

  • Median terminal portfolio: roughly £2.3m (real)
  • 10th-percentile terminal portfolio: roughly £80k (real)
  • 90th-percentile terminal portfolio: roughly £5.8m (real)
  • Failure rate: ~13%

• At 3.5% withdrawal:

  • Median terminal portfolio: roughly £3.7m (real) — 60% higher
  • 10th-percentile terminal portfolio: roughly £450k (real) — 5.6× higher
  • 90th-percentile terminal portfolio: roughly £8.1m (real) — 40% higher
  • Failure rate: ~3%

The relative improvement is largest in the worst-case cohorts — exactly where it matters for planning. A 5.6× larger 10th-percentile terminal portfolio means the difference between "barely scraping through" and "comfortable margin for unexpected expenses." See our 40-year horizon article for the underlying methodology.

Why the leverage is so asymmetric

Two compounding effects:

1. Withdrawal compounding. Drawing 3.5% × £1.14m = £40k vs 4% × £1m = £40k — same annual draw, but the lower rate means you're drawing a smaller fraction of a bigger pot. The pot has more left over each year to compound forward.
2. Sequence cushion. When markets crash in year 3, a 3.5% withdrawal at a £1.14m starting portfolio is still drawing £40k from what's now £850k. That's 4.7% — uncomfortable but survivable. The same year for a 4% withdrawer at £1m: drawing from £750k, that's 5.3%. The lower starting rate gives you more headroom against bad sequences.

The two effects multiply. Over a long horizon, the difference between "survivable" and "depleted" can hinge on exactly this kind of small starting-rate gap.

The reverse direction

The math works the other way too. Going from 3.5% to 3.0% gains you another 17% lower FIRE number requirement (£1.33m), but the marginal sequence-risk benefit shrinks. Every 0.5% lower delivers diminishing additional safety once you're below about 3.25%, because at that point you're already surviving all historical cohorts.

For a useful continuum:

• 4.0%: ~75% historical survival at 50 years (per our 50-year article)
• 3.75%: ~85% survival
• 3.5%: ~93% survival
• 3.25%: ~98% survival
• 3.0%: 100% survival

The biggest survival jump is from 4% to 3.5%. Below that, you're paying for marginal additional safety.

When it isn't worth the extra accumulation

For some FIRE planners, working 1.8 more years to drop from 4% to 3.5% is the wrong trade:

• High earners with low expenses. If you can save £100k+/year, 1.8 years is a £180k+ accumulation gain — possibly more than the additional buffer you'd build.
• Pre-retirement burn-out. If you genuinely can't tolerate the work, going at 4% with flexibility is better than waiting at 3.5%.
• Strong external-income picture. State pension + part-time work in the early years may make the sequence-risk concern less acute, justifying the higher rate.

The practical takeaway

The 0.5% conversation isn't about which number is "right." It's about how much extra working time you're willing to trade for incremental sequence-risk protection. For most planners, dropping from 4% to 3.5% is worth roughly 1.5–2 years of work. Dropping from 3.5% to 3.25% probably isn't.

Run both rates against your own plan in our withdrawal survival tool — the survival curves and terminal-wealth distributions will show you the trade visually.