How to calculate it
Start with household income after tax and subtract fixed expenses such as housing, insurance, transport agreements, childcare, debt and subscriptions.
The remainder covers food, clothing, leisure, gifts, personal care and unexpected purchases. Keep definitions consistent so months can be compared.
Use three ordinary months as your guide
Review at least three normal months, remove one-off expenses and use the median for variable spending. This is more realistic than one unusually cheap or expensive month.
If no room remains for a small buffer, adjust fixed costs, variable limits or the savings target until the plan works in practice.
Make it practical with a daily amount
A daily amount makes a monthly figure easier to use. Remember to reserve money for larger variable purchases later in the month.