How big should an emergency fund be?

The rule of thumb is three to six months of essential expenses, stretching to six to twelve months when income is unpredictable.

That sentence contains the whole guide, and the two words doing the work are essential expenses. Almost every version of this advice you will hear gets the unit wrong, and the unit is what decides whether the target is achievable or absurd.

Not income. Not total spending.

Three common versions, only one of which is right:

• Months of income — wrong, and much too big. Your income includes taxes, retirement contributions and discretionary spending. If you lose your job you are not replacing your gross salary; you are covering what you must pay.
• Months of total spending — wrong, and still too big. Total spending includes holidays, restaurants, subscriptions and the new sofa. In a genuine emergency, most of that stops immediately.
• Months of essential expenses — right. Housing, utilities, food, transportation, insurance, minimum debt payments, childcare, medication. Everything you would still be paying in a bad month.

The gap between these is not small. A household earning $8,000 a month might spend $6,000 and have essential expenses of $4,000. Six months of income is $48,000. Six months of essentials is $24,000. The second is a target you can reach this year; the first is a reason to give up.

So the first task is not saving. It is working out your essential monthly figure, which most people have never done and which usually comes in lower than they feared.

Which band you are in

The three-to-six range and the six-to-twelve range are about how predictable your income is and how fast you could replace it:

• Very stable — salaried, in-demand field, two incomes. The bottom of three to six. A second income means one job loss does not take everything.
• Typical — salaried, one or two incomes. The top of the three-to-six range, and the usual answer for a salaried household.
• Single income supporting others — six to twelve. One income covering dependants has no second earner to fall back on.
• Variable — self-employed, commission, contract. Six to twelve, and the upper half of it. Income that arrives unevenly needs a buffer that absorbs the unevenness as well as the emergencies.

The emergency fund calculator takes your essential expenses and your income stability and gives a target inside the right band, along with how long it takes to get there at your current saving rate.

Where the money should sit

Two requirements, in this order: available the day you need it, and not worth less than you put in.

That rules out almost everything except a savings or money market account. Not invested — a market fall and a job loss have an unpleasant habit of arriving in the same quarter, and an emergency fund that dropped 20% right when you needed it was not an emergency fund.

It does not rule out earning something. A high-yield savings account pays several percentage points more than a large bank's default rate for the same insured deposit, which on $25,000 is real money for a form you fill in once. See what a savings account really earns.

Keep it in a separate account from day-to-day money. Not for psychological reasons — because money in your checking account gets spent by accident.

What counts as an emergency

A useful test: unexpected, necessary and urgent. All three.

A car repair you need to get to work is all three. A holiday is none of them. Replacing a failed water heater is all three. Replacing a working one is not.

The failure mode is not people raiding the fund for holidays. It is a slow drift where the fund becomes a general-purpose buffer, never gets replenished, and is at $800 when something real happens.

What to do with this

1. Add up your essential monthly expenses. One sitting. This is the step that makes the rest possible.
2. Pick your band from how predictable your income is.
3. Start with one month. A full six-month target is discouraging from zero, and the first $2,000 removes most of the situations where a small problem becomes a credit card balance at 24%.
4. Automate it, then stop thinking about it.
5. Capture the employer match first, if there is one. A 50% or 100% match outranks almost everything — see the 401(k) match question.
6. Replenish after use. The fund is only a fund if it refills.

Three to six months of essential expenses. Availability over yield. And the first thousand dollars does more work than any thousand after it.

Sources: the three-to-six-month rule of thumb, and the six-to-twelve band for unpredictable income, are the conventional planning guidance this site's calculator implements; the bands and the situation mapping are documented in the calculator's own source. FDIC insured-deposit figures from FDIC, deposit insurance.