A Grocery Budget Calculator

The formula this calculator uses

Weekly budget = household size x spend per person per week

W

The weekly grocery budget for the whole household

n

The number of people being fed

s

The cost of one person's food for one week

How to check the result by hand

1. 1

   Count the household

   Count everyone who regularly eats from the grocery shop, including children. Partial cases, such as a child who is away part of the week, are usually easier to handle as a whole person than as a fraction.

2. 2

   Find a realistic per person weekly rate

   Use several weeks of receipts rather than one. Divide the total food spend by the number of people and by the number of weeks covered. One unusual week, either a big stock-up shop or a week of eating out, will distort a single week badly.

3. 3

   Multiply to get the weekly budget

   Household size times the per person rate gives the weekly figure. Four people at 95 dollars is 380 dollars a week.

4. 4

   Annualise, then divide by twelve

   Multiply the weekly figure by 52 for the annual budget, then divide by 12 for the monthly one. Do not multiply the weekly figure by four; that understates the monthly requirement by roughly a week every three months.

5. 5

   Compare the annual figure against income

   Divide annual grocery spend by annual household income. If the share looks high, check whether non-food supermarket items are being counted as groceries before concluding the food spend itself is the problem.