How big your emergency fund should be
An emergency fund covers your essential expenses if your income stops or a big unexpected bill arrives. The usual guideline is three to six months of essentials: housing, utilities, food, transport, insurance and minimum debt payments. Leave out spending you could cut in an emergency.
Where to keep it
Somewhere safe and available within days, separate from your everyday account. It is not an investment: its job is to be there when you need it.