Household Budget Calculator

Start from take-home income, list every commitment, sort them into needs, wants and savings, and compare against a target split. The listing is the hard part — most budgets fail because a category was forgotten, not because the arithmetic was wrong.

A need is something you would still pay in a bad month: housing, utilities, basic food, transport to work, insurance and minimum debt payments. Everything else is a want, including the parts of those categories above the minimum.

Assign it before the month starts. Unallocated money is not spare — it is money without a job, and it gets spent by default. That is the entire premise of zero-based budgeting.

Monthly at first, then quarterly once it is stable. Reviewing against what actually happened rather than what was planned is the part that changes behaviour, and it is the part most people skip.

Net, always. Gross income is the number for a mortgage application; a budget can only allocate money that reaches your account.

That is extremely common where housing is expensive, and it is not a failure. The useful question becomes which of wants or savings absorbs the difference, and making that choice deliberately beats letting it happen by default.

About three months. The first month's figures are guesses, the second corrects them, and by the third the categories reflect what actually happens. Most people abandon it in month two.

Categories tell you what you spend on; accounts tell you what is available. Separate accounts for bills, spending and savings enforce the categories physically, which works better than discipline for most people.

Budget on your lowest recent month and treat everything above it as unallocated. The alternative — budgeting on the average — leaves you short in every below-average month.

One month of expenses held in the current account so you are always spending last month's income. It converts every timing problem into a non-event, and it is the single most useful thing after an emergency fund.

The budget usually has to be joint even where the accounts are not, because shared costs need a single view. A common arrangement is proportional contributions to a joint account for shared costs, with the remainder individual.

Irregular annual costs — insurance renewals, car servicing, professional fees, Christmas. They are entirely predictable and they are budgeted for in the month they land, which is what makes them feel like emergencies.