How big should my emergency fund be?

How many months of ordinary outgoings your savings already cover, what the target costs, and how long the gap takes to close. It sizes the fund against what you spend, never against what you earn, and it assumes no return on the balance — the fund is held where it can be reached, not where it grows.

Your fund covers 1.3 of the 6 months you set. Adding 1,500 a month, you reach 54,000 in 28 months, assuming your outgoings hold.

Months of cover is the fund divided by what you spend in an ordinary month. The target is the months you chose multiplied by those same outgoings, and the gap is whatever the fund has not reached yet.

The input is outgoings and not pay, and that is the whole argument of the guide this sits under. A household sizing six months against take-home pay is building to a target the rule never set, and spending the extra months getting there. If your outgoings are well below your pay, the correct fund is smaller than the internet will tell you.

No return is assumed on the balance. That is a position rather than an omission: an emergency fund's job is to be reachable within a day at a value that cannot have fallen overnight, which rules out anything that has to be sold. A fund earning a modelled return is a fund invested in something you might have to sell on the exact day you need it.

months covered = fund ÷ monthly outgoings

The target is that number of months multiplied by the same outgoings.

What it assumes

• Outgoings stay flat while you build the fund. In practice the number you are sizing against is the one most likely to move.
• The balance earns nothing. An emergency fund is held where it can be reached, not where it grows, and the guide says why.
• The monthly addition is made every month without interruption. A month missed moves the arrival date by more than a month, because nothing is compounding to catch up.