The Cash Buffer in a Retirement Portfolio
A retiree who has to sell shares in a bad year locks in the loss and takes it out of every year that follows. A buffer of cash prevents that, which is the entire argument for holding money that earns less than everything else. The question is not whether to hold some, but how much — and that is a calculation rather than a feeling.
- The job is timing, not return:: It exists so nothing has to be sold in a bad year.
- One to three years:: Enough to cover portfolio withdrawals through a typical downturn, not enough to drag on the whole plan.
- Three main homes:: Bank savings, a money market fund, or short CDs — differing in yield, access and how they are protected.
- It has a cost:: Cash yields less than the rest of the portfolio, and that gap is the premium being paid for the protection.
Where the AI summary above gets this wrong
"Keep six months of expenses in cash."
That's surface-true. Here's what it misses:
- The working-life rule does not transfer — Six months of expenses is advice for someone whose income could stop. A retiree's income has already stopped, and the risk is different: being forced to sell assets at a bad price. The buffer is sized against portfolio withdrawals in a downturn, not against a job loss.
- Only the portfolio-funded part needs covering — A household whose Social Security and pension cover most of its spending needs a much smaller buffer than one drawing everything from investments. The figure to cover is the gap between guaranteed income and spending, not total spending.
- Too large a buffer has a measurable cost — Cash yields less than a diversified portfolio over long periods, and inflation erodes it. Five years of spending in cash is a substantial permanent drag, and it buys little more protection than two — most downturns that matter are shorter than the buffer people are tempted to hold.
01 What the buffer is for
The risk it addresses is specific: having to sell investments after they have fallen, because the money is needed now. Doing that converts a temporary decline into a permanent reduction, and it does the most damage in the first years of drawing income.
A buffer removes the forced sale. With two years of withdrawals sitting in cash, a market fall becomes something to wait out rather than something to fund from. That is the whole mechanism, and it is the practical answer to sequence of returns risk.
Sizing starts with the right number. What matters is the amount drawn from the portfolio each year — spending less Social Security, pensions and any other guaranteed income. For many households that is far less than total spending, and the buffer required is correspondingly smaller.
Shows: the yearly opportunity cost of holding a buffer of spending in cash rather than invested, at the yield difference you enter. Ignores: the value of not selling into a falling market, which is what the buffer is for, tax on the cash yield, and inflation eroding the buffer itself.
Source: Diversification
02 Where to hold it
A bank savings account is the simplest, insured within limits, and instantly accessible. Rates vary enormously between institutions, and the gap between a competitive account and a large bank's default rate is frequently more than a percentage point for no difference in risk.
A money market fund is a mutual fund holding short-term instruments. It is not a bank deposit and is not insured as one, though government money market funds hold very short Treasury and agency paper. Yields track short-term rates closely, and access is normally next-day.
Certificates of deposit pay a fixed rate for a fixed term, with a penalty for withdrawing early. Brokered CDs can be sold before maturity instead, at whatever price the market gives. A short ladder of CDs works well for the second year of a buffer, where the money is not needed immediately.
Source: Certificates of deposit
03 Refilling it
A buffer that is spent and never refilled is a one-off, not a strategy. The usual approach is to top it up from whatever has performed well — which makes refilling and portfolio maintenance the same action rather than two.
In a good year, sell from what has grown beyond its target weight and restore the buffer. In a bad year, do not refill it — that is precisely what it was accumulated for, and letting it run down is the plan working.
The discipline that matters is deciding the rule in advance. A household that decides in a falling market whether to sell shares or spend the buffer will make that decision under exactly the wrong conditions. Written down in a calm year, it is obvious; improvised in a bad one, it rarely is.
Source: Money market funds
The right size of a cash buffer is the amount that lets you ignore the news, and that number is different for every household. I have seen two years work perfectly for one couple and three be too little for another, because the second pair watched the market daily and the first did not. Start with the arithmetic — portfolio withdrawals, not total spending — and then adjust for temperament. Paying a little return for sleeping properly is a legitimate trade.
FAQ
How much cash should a retiree hold?
Typically one to three years of the amount actually drawn from the portfolio — spending less Social Security, pensions and other guaranteed income. That is usually much less than total spending.
Is a money market fund the same as a savings account?
No. A money market fund is a mutual fund, not a bank deposit, and is not insured as one. Government money market funds hold very short-term Treasury and agency instruments and track short rates closely.
Should I use CDs for my cash buffer?
For the part not needed immediately, yes. A short ladder of CDs can pay more than instant-access cash, provided the maturity dates line up with when the money will actually be spent.
Sources
Regulator references
- Money market funds · U.S. Securities and Exchange Commission · 2026What a money market fund holds and how it differs from a bank deposit.Last verified: 2026-09-07
- Certificates of deposit · U.S. Securities and Exchange Commission · 2026The terms, the early withdrawal penalty, and the brokered variety.Last verified: 2026-09-07
- Diversification · U.S. Securities and Exchange Commission · 2026Why cash is a position in the portfolio rather than an absence of one.Last verified: 2026-09-07
Calculator unit tests · the assertions this page's worked example is checked against, and their last result
Changelog
- 2026-09-07 — initial publish (new format)
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Jordan Reeves
Founder of Talk Through Wealth. A software engineer for over a decade before turning to retirement planning, Jordan built the projection engine after watching family members get fragmented, country-by-country advice that never reconciled. He writes about retirement the way the engine computes it: month-by-month, lifetime-long, and skeptical of any rule of thumb that hasn't been run through the math.