Emergency Fund Calculator – Size Your Safety Net and Plan How to Build It
An emergency fund is cash you set aside to keep paying the essentials if your income stops, or when a large, unavoidable bill lands at the worst moment. This emergency fund calculator answers four questions in order: how big your fund should be, how many months your savings would last today, how many months you should aim for, and how to get there with a monthly saving plan.
Start with essential expenses, not total spending
The target is built from what you would still have to pay if your income stopped: housing, utilities, groceries, transport, insurance, the minimum payment on each debt, phone and internet, childcare and medical costs. Leave out retirement contributions and other saving (you would pause them), dining out and subscriptions you would cancel. Using this lean version gives a smaller, more reachable target that still covers what matters. Amounts can be weekly, fortnightly, quarterly or yearly; each one is converted to an average month, so groceries of 120 a week count as 120 × 52 ÷ 12 = 520 a month.
How continuing income and one-off costs change the target
If some money would keep arriving, such as a partner's pay, rental income or unemployment benefits, your fund only has to cover the monthly gap: gap = max(0, essentials − continuing income). Income that stops after a set number of months, like benefits, is counted only for those months. One-off costs, such as an insurance deductible or an urgent car repair, are added to the target once.
Take essentials of 3,025 a month, a partner earning 1,800 and benefits of 900 for four months. The gap is 325 for months 1–4 and 1,225 after that. Six months of cover therefore needs 4 × 325 + 2 × 1,225 = 3,750, plus 2,500 of one-off costs, for a target of 6,250. Without the continuing income the same six months would need 20,650.
Reading the coverage scale and runway chart
Months of cover (your runway) shows how long your savings would last if your income stopped today. The calculation first sets aside the one-off costs, then pays each month's gap, so savings equal to the target always give exactly the number of months you chose. The coverage scale marks where you are and where your target is, next to a neutral band for the common three-to-six-month range. The runway chart draws your savings falling month by month, with a dashed line for a full fund and a vertical marker wherever a source of income ends, which is where the slope gets steeper.
Choosing how many months to cover
Three to six months of essentials is the rule of thumb most often repeated in personal-finance guidance, but your situation matters more than any single number. The optional Help me choose panel asks five questions about how you are paid, how many people earn, whether anyone depends on you, how long a replacement job might take and whether anyone has an ongoing health condition. It starts at 3 months and adds points for each risk factor, giving a suggestion between 3 and 11 months. It is a transparent rule of thumb, not an official formula, and it never changes your months on its own.
Building the fund in milestones
A full fund can feel far away, so the plan breaks it into steps: one month of cover, three months, six months, then fully funded. Enter what you can save each month to see when each milestone arrives, or pick a finish date to see the monthly amount required. An optional interest rate (APY) is converted to a monthly rate with r = (1 + APY)^(1/12) − 1, and each deposit is assumed at the end of the month. The target and any required monthly amount are rounded up, so the tool never understates what you need.
Review it once a year
The target is in today's money. Revisit it at least once a year, and whenever your rent, household, job or insurance changes. After you use part of the fund, the same plan shows how long it will take to top it back up.