Emergency Fund Calculator

An emergency fund is one of the few personal finance moves with no real downside: it costs you slightly less in long-run returns than fully investing the money, and it buys you something money usually can't, which is the option to walk away from a bad situation. Our emergency fund calculator does the maths so you know exactly how big yours should be and how long it will take to build at your current saving rate.

The two questions every reader asks are "how much?" and "how long?". The calculator answers both, plus a third one most articles skip: at what balance does your savings interest start getting taxed, and is a Cash ISA the better home? This guide walks through every input and every output.

Contents

• What the emergency fund calculator does
• How to choose your months of cover
• Why monthly expenses, not income
• The Personal Savings Allowance trap
• Worked example: £2,000/month expenses, £200/month saving

What the emergency fund calculator does

Two computations and one warning:

1. Target amount. Your monthly essential expenses multiplied by the months of cover you choose (3, 6, 9 or 12). The output is the pound figure you're aiming at.
2. Time to target. Starting from your current savings, the calculator simulates each month: add your monthly contribution, apply savings interest, check if you've hit the target. The output is the number of months and an estimated calendar date.
3. Personal Savings Allowance warning. If you've selected an easy-access savings account (rather than a Cash ISA), the calculator estimates the annual interest you'd earn on the target balance. If that exceeds £500, it flags that you may pay tax on the excess and recommends moving to a Cash ISA.

The output is shareable via URL, so you can model different scenarios (3 months vs 6 months, current vs ideal contribution) and send the link to a partner.

How to choose your months of cover

The standard advice is "3 to 6 months of expenses". That's a useful range, but it's worth choosing deliberately rather than picking the middle:

• 3 months is the floor. It works for stable salaried jobs with strong demand for your skills, dual-income households where one partner could cover the other's gap, or anyone with a substantial second buffer (parents who'd front money in a crisis, large investment portfolio you could draw from).
• 6 months is the sensible default for most UK households. It covers a typical job search timeline, gives you negotiating power on the next role, and absorbs most life events (illness, bereavement, urgent home repairs) without forcing a fire sale of investments.
• 9 to 12 months is for genuinely volatile situations: self-employment with lumpy income, contractors, single-income households with dependants, or people working in a sector going through layoffs. The opportunity cost (money sitting in cash that could be invested) is meaningful at this level, but so is the cost of being forced into a bad job at a bad time.

The calculator lets you toggle between all four to see how the target moves. The £4,000 difference between a 6-month and 12-month fund at £2,000 monthly expenses is real money, but so is the difference in how long the fund will support you.

Why monthly expenses, not income

The calculator asks for essential monthly expenses, not gross or net income. This matters.

In an emergency you cut discretionary spending: the gym, the streaming services, dining out, holidays, anything that isn't keeping a roof over your head and food in the fridge. The fund only needs to cover the essentials: rent or mortgage, council tax, energy, water, broadband (if you need it for job hunting), groceries, transport to interviews, and basic insurance.

For many UK households, essentials are often in the region of 60-75% of total spending. A household with £3,500 in total monthly outgoings might have essential expenses of around £2,200. Sizing the fund against £2,200 instead of £3,500 cuts the target by roughly 37% without making you any less covered in a real emergency.

If you don't know your essential figure, run a quick audit: list every recurring expense from your last bank statement and circle the ones you genuinely couldn't cancel for six months. The total is your essentials.

The Personal Savings Allowance trap

Here's the part most calculators don't mention. UK savers have a Personal Savings Allowance:

• £1,000 per year if you're a basic-rate taxpayer
• £500 per year if you're a higher-rate taxpayer
• £0 if you're an additional-rate taxpayer

Interest above the allowance gets taxed at your marginal rate. So a higher-rate taxpayer earning £600 in savings interest pays 40% tax on the £100 above the £500 allowance: £40 lost.

Easy-access rates have typically sat in the 4-5% range during 2025/26, though rates change frequently - check current best-buy tables before committing. At 4.5%, you only need around £11,111 of savings to generate £500 of interest. For a 6-month emergency fund of £12,000, a higher-rate taxpayer would already be over the threshold. For a 12-month fund the maths gets worse.

One option is to hold the emergency fund in a Cash ISA instead of an easy-access savings account. Cash ISA interest is tax-free regardless of the size of the balance, and many providers offer rates broadly comparable to easy-access accounts. The calculator's account-type toggle reflects this: switch to "Cash ISA" and the PSA warning disappears.

A non-ISA account can still suit you if your ISA allowance is being used for higher-yielding Stocks and Shares ISA contributions and you've maxed the £20,000 limit. Otherwise, for many savers the Cash ISA tends to be a cleaner home for emergency-fund cash. This is general information, not personal advice.

Worked example: £2,000/month expenses, £200/month saving

Plug in monthly essentials of £2,000, 6 months of cover, current savings of £0, monthly contribution of £200, and a 4% rate in a Cash ISA.

The calculator returns:

• Target: £12,000
• Monthly contribution to reach target: 53 months (about 4 years 5 months)
• Total interest earned along the way: roughly £950
• PSA warning: not triggered (Cash ISA is tax-free)

Now bump the monthly contribution to £400 and re-run:

• Same target
• Months to target: 28 (about 2 years 4 months)

That's the calculator's most useful insight. The single biggest lever isn't the interest rate, it's the monthly contribution. Doubling the contribution roughly halves the time to target. If your current path puts the fully-funded date five years away, the question to ask isn't "what rate could I get?" but "how do I find another £100 a month?".