The calculator
A 4.0% target with a +5.0% / −2.5% clamp starts at $40,000 and ends at $50,801, with a portfolio of $1,270,036.
Auf Deutsch: Vanguard Dynamic Spending Rechner
How it works
Vanguard calls this its dynamic spending strategy, and its research papers describe it as a dynamic spending approach that sits between a fixed dollar amount and a fixed percentage. This dynamic spending calculator follows Vanguard's published rule: a target of rate × current portfolio, then a clamp so the real change versus last year stays inside a ceiling and a floor. The usual defaults are +5% and −2.5%. After a 50% crash the target would collapse; the floor stops spending falling more than 2.5% that year. The Guyton-Klinger calculator is the discrete alternative.
The rule exists to sit between two rules that each fail in an obvious way. Constant-dollar 4% ignores the portfolio completely and keeps writing the same cheque into a crash. A pure percentage of the balance tracks the portfolio perfectly and hands you a 30% pay cut the year the market halves. Dynamic spending follows the balance but limits how fast your income is allowed to move.
Calculating it by hand
The rule needs one multiplication and two comparisons a year, which is why it works in a spreadsheet as well as in a simulator.
- Target. Multiply your target rate by the current portfolio value, not the value you started with.
- Band. Take last year's actual spending and raise it by inflation. The ceiling is that figure +5%; the floor is that figure −2.5%.
- Clamp. If the target lands inside the band, spend the target. If it lands outside, spend the nearer edge of the band.
A worked year: $1,000,000 at a 4% target spends $40,000. The portfolio then falls to $700,000, so next year's target is $28,000, a 30% cut. With 2% inflation, last year's spending indexes to $40,800 and the floor is 2.5% below that, $39,780. You spend $39,780, not $28,000. The clamp absorbed the crash, and the portfolio paid for it.
Dynamic spending strategy example
Carry that worked year forward. Same 4% target, 2% inflation, and the portfolio value on each annual review date:
| Year | Portfolio at review | 4% target | Allowed range | You spend |
|---|---|---|---|---|
| 1 | $1,000,000 | $40,000 | First year | $40,000 |
| 2 | $700,000 | $28,000 | $39,780 to $42,840 | $39,780 |
| 3 | $900,000 | $36,000 | $39,561 to $42,604 | $39,561 |
| 4 | $1,200,000 | $48,000 | $39,344 to $42,370 | $42,370 |
In year three the portfolio has recovered to $900,000, but the $36,000 target is still below the floor, so spending slips another 2.5% in real terms rather than jumping back. In year four the portfolio reaches $1,200,000 and the target of $48,000 is above the ceiling, so the raise stops at $42,370. Income moves a little every year and never lurches, while the portfolio absorbs the difference in both directions.
Dynamic spending through history: 1966 and the good years
We replayed every 30-year window from 1928 to 1996 (69 start years) on $1,000,000 in 60% stocks, 35% bonds and 5% cash, comparing a constant-dollar 4% withdrawal with the dynamic spending rule at a 4% target. Lifetime spending is the 30-year total in start-year dollars.
| Retired in | Constant-dollar 4% | Dynamic spending: lifetime spending | Dynamic spending: lowest year | Dynamic spending: left after 30 years |
|---|---|---|---|---|
| 1929 | Lasted, $1,189,367 spent | $895,518 | $22,344 | $624,987 |
| 1966 | Ran out of money | $830,267 | $18,954 | $501,469 |
| 1973 | Lasted, $1,173,229 spent | $882,988 | $23,002 | $662,663 |
Retiring in 1966 is the bad case: flat markets and high inflation for a decade. The fixed $40,000 ran out of money, while the dynamic spending rule cut gradually, spent $18,954 in its leanest year and still had $501,469 left. The good years are the other half of the trade. In the best window, dynamic spending paid out $2,172,881 over 30 years against $1,190,089 for the fixed 4%, because it raised spending as the portfolio grew. Across all 69 windows it spent more than the fixed 4% in 42 and never ran out; the fixed 4% ran out in 4.
What the clamp costs
That last sentence is the part most comparisons leave out. Softening the cut has to be funded from somewhere, and the somewhere is the balance.
We ran the rule against three others across 5,000 seeded 30-year retirements on an identical $1,000,000 portfolio, changing nothing but the spending rule. Unclamped percent-of-balance ran out of money in 0.0% of them, because a percentage of a positive number is always positive, and it pushed real spending below $30,000 a year in 72.5% of them. Dynamic spending ran out in 10.0% of the same worlds. The clamp is what makes it able to fail, and the same clamp gives it the highest spending floor of the flexible rules.
Against constant-dollar 4% on the same worlds it delivered $17,830 more lifetime real spending in the median world and $198,702 less in the worst tenth. Which of those two numbers matters more is a question about you, not about the rule. The full study has the parameter stress and the 1928–2025 historical replay, including the windows where the ordering reverses.
Pros and cons of the dynamic spending strategy
| Pros | Cons |
|---|---|
| Spending follows the portfolio, so a long bad stretch is met with cuts. | Those cuts add up: in the 1966 window the leanest year was under half the first. |
| No single-year cut is bigger than 2.5% in real terms. | The floor that limits cuts also means it can run out, unlike a pure percentage. |
| Good markets raise spending, up to 5% a year in real terms. | Income is less predictable than a fixed, inflation-adjusted withdrawal. |
| One multiplication and two comparisons a year; works in a spreadsheet. | It treats all spending as flexible, so essentials need a separate floor or income. |
Versus the other rules
Guyton-Klinger guardrails leave spending untouched most years and then make a discrete 10% cut when the withdrawal rate drifts outside a band: fewer adjustments, bigger ones. Dynamic spending is the opposite shape: it adjusts a little every year and never makes a 10% jump. Neither is safer in the abstract. Rails put occasional lumps on your lifestyle; the clamp puts a slow cut or a slow raise on it. The Yale endowment rule blends last year's spending with the target instead of clamping the change. A side-by-side of nine withdrawal rules sets all of them against the same portfolio.
The locked-rate sibling is the 4% rule calculator. Unlock the rate on the safe withdrawal rate calculator. Spend a rising share of what is left with the VPW calculator, or set year one from valuations with the CAPE-based withdrawal calculator (the CAPE-based withdrawal guide explains the rule). The accumulation identity is the FIRE calculator and the Coast FIRE calculator; a distribution of endings is the Monte Carlo retirement calculator. The same average with a crash first versus last is the sequence of returns risk calculator. The endowment-smoothing explainer is the Yale spending rule.
These rules set spending before tax. The retirement tax calculators show what each withdrawal costs once Social Security, RMDs and IRMAA are counted.
When to use Vanguard dynamic spending
Use the clamp when a 10% spending cut would be a household crisis but a 3% cut would not. Use guardrails when you would rather leave spending alone until you have to change it. Use a fixed, inflation-adjusted withdrawal for the part of your spending you cannot cut at all, such as housing or a health insurance premium, and accept that the portfolio then carries all of the risk. The two also combine: a fixed floor for essentials and a dynamic rule for everything else.
Assumptions
One return every year, no fees, no taxes. The clamp is applied in real terms (last year × (1 + inflation), then ± the cap). A constant return will not exercise the floor the way a real crash would, which is exactly why the simulated figures above come from 5,000 varying paths rather than from this page's single-path model.