Emergency fund calculator
How long does it take to build a buffer for unexpected costs? Enter what you spend per month, how many months of spending you want to set aside, what you already have and what you can add each month.
Two worked examples
With €2,000 of spending a month and a target of 3 months, the buffer is €6,000. Starting from €0 and adding €500 a month, with no interest, it takes 12 months. Adding €200 a month instead takes 30 months.
A larger buffer: 6 months of €2,000 is €12,000. Starting from €1,000, adding €300 a month and entering 2% interest a year, the tool reaches it after 36 months, at €12,183. Of that, €1,000 was already there, €10,800 was added and €383 is interest. The 2% is only an example rate.
How it calculates. The target is your monthly spending times the number of months you choose. The tool then adds month by month: new balance = old balance × (1 + interest ÷ 12) + monthly addition, until the balance reaches the target. Without interest it is simply the gap divided by the monthly addition, rounded up to a whole month.
How to read the result. The answer is the number of months until the target is first reached, with the balance in that month. On a short horizon, interest makes little difference: in the second example it is €383 over three years. What you add each month decides most of the time it takes.
What it is not. A calculation with your own numbers, not advice. How many months of spending to keep aside depends on your situation, and the tool says nothing about it, so the number of months is left empty on purpose. Interest rates can change at any time, and tax and inflation are not included. After 50 years the tool stops.
Where it comes from. Only the formula and your own input. The tool uses no external data and stores nothing.
Questions about the emergency fund
How many months of spending should I set aside?
Only you can decide that, which is why the field is left empty. It depends on things like how steady your income is, your fixed costs and who depends on you. Nobody can give one number for everyone. If you are unsure, a qualified adviser can help you decide.
Do I have to enter interest?
No. Without interest the answer is the gap divided by what you add each month, rounded up to whole months. If your savings account pays interest, you can enter that rate; the 2% in the second example is only an example rate, and rates can change at any time.
Why does a smaller monthly amount take so much longer?
Because the time is the gap divided by the monthly amount. In the first example the gap is €6,000: at €500 a month that takes 12 months, at €200 a month 30 months. Reducing the monthly amount by 60% makes the wait 2.5 times as long.
How the calculation works
The target is your monthly spending times the number of months you choose. The tool then walks forward one month at a time. Each month it first adds a month of interest to the balance (the yearly rate divided by 12, if you entered one) and then adds your monthly amount, rounding to the cent. The first month in which the balance is at or above the target is the answer. If you start at or above the target, the answer is 0 months, and the tool stops after 50 years if the target is not reached.
One line of arithmetic with no interest: €1,800 of spending times 4 months is €7,200. You already have €1,500, so the gap is €5,700. At €250 a month, 5,700 ÷ 250 = 22.8, which rounds up to 23 months. After 23 months the balance is €1,500 + 23 × €250 = €7,250, just over the target.
Two situations with the maths filled in
These are made-up situations. The amounts and the interest rate are chosen only for the example, and nothing here suggests how much anyone should set aside.
Situation 1: a bigger monthly amount. Using the €7,200 target and €1,500 already saved from above, adding €400 a month instead of €250 turns the gap of €5,700 into 5,700 ÷ 400 = 14.25, so 15 months, ending at €7,500. That is 8 months sooner for €150 more a month.
Situation 2: interest on a larger target. Someone spends €2,400 a month and wants 5 months of it, which is €12,000. They have €3,000 and add €400 a month. Without interest the target is reached after 23 months, at €12,200. With an example rate of 3% a year it is reached after 22 months, at €12,204. Of that, €3,000 was there at the start, €8,800 was added and about €404 is interest. A rate that is the same for every month is itself a simplification. Adding €600 a month instead, with the same 3%, reaches the target in 15 months.
| Monthly addition | Interest | Months | Balance at the end |
|---|---|---|---|
| €400 | 0% | 23 | €12,200 |
| €400 | 3% (example) | 22 | €12,204 |
| €600 | 3% (example) | 15 | €12,274 |
Common mistakes when reading the result
- Treating the number of months as a recommendation. The tool shows how long a chosen amount takes; it does not say how many months anyone needs.
- Leaving out irregular costs such as repairs or insurance, which makes the monthly spending look lower than it is.
- Assuming the monthly amount never changes. A month in which you have to use the buffer is not shown.
What the calculation leaves out
The tool assumes that your spending, your monthly amount and the interest rate stay the same every month, which real life rarely does. It leaves out rising prices, which can make the same lifestyle cost more later and so raise the target over time. It leaves out tax and any limit on how much a bank or account will hold or protect. It assumes you add the same amount every month and never withdraw, so a month in which you have to use the buffer is not shown. It counts interest as paid monthly at a twelfth of the yearly rate, while real accounts may pay differently, and it only gives whole months. Nothing here says how many months of spending you should aim for.
Further reading: