Build a grocery list and see the total cost instantly.
A grocery list total is item count times average price, and the reason estimates go wrong is almost never arithmetic — it is the average. People anchor on the price of staples and forget that one or two premium items drag the mean upward, which is why a twenty-four item list that feels like a sixty dollar shop rings up at eighty-five. Sales tax then applies on top, and its treatment of food varies enormously: many jurisdictions exempt unprepared groceries entirely, others tax them at a reduced rate, and prepared or hot food is usually taxed at the full rate even in states that exempt everything else. Working out how many items the budget covers gives a clean stop rule at the shelf.
List total against a budget
Subtotal = item count x average price; tax = subtotal x tax rate / 100; total = subtotal + tax; items affordable = floor(budget / (total / item count))
Because the average is usually optimistic. Meat, cheese, coffee and alcohol sit far above the median grocery item, so a handful of them lifts the mean more than people expect. Estimate the mean from a past receipt rather than from memory.
It varies widely. Many places exempt unprepared food entirely, some apply a reduced rate, and prepared, hot or restaurant-style items are usually taxed at the standard rate. Set the rate to zero if your groceries are exempt.
Use the affordable-items figure as a hard count. Knowing the budget covers twenty-two items rather than twenty-four tells you to drop two before you reach the till, not after.