Small pack Cheaper for you
£1.40 for 500 g
- Shelf price
- £2.80 per kg
- You use
- 500 g in 5 days
- Thrown away
- nothing
- Real price
- £2.80 per kg
- Costs you
- £8.52 a month
Bulk vs small pack
The big pack is cheaper per kilo on the shelf. Is it still cheaper once you count what goes off before you finish it?
What you really pay
The small pack saves you about £4.87 a month at your usage.
Bulk pack
£2.20 for 1 kg
- Shelf price
- £2.20 per kg
- You use
- 500 g in 5 days
- Thrown away
- 50%
- Real price
- £4.40 per kg
- Costs you
- £13.39 a month
The bulk pack beats the small one only if you use at least 79% of it before it spoils, which means getting through about 157.14 g a day.
Counting what you actually use
The price per kilo on the shelf assumes you use every last bit. At home, opened packs go stale, mouldy or past their date, and whatever goes in the bin was still paid for. This tool works out how much of each pack you get through before it spoils, from how fast you use it and how long it keeps:
Real unit price = pack price ÷ the amount you use before it spoils
In the yogurt example, a 500 g pot for £1.40 is finished in five days, so you pay the shelf rate of £2.80 per kg. The 1 kg tub at £2.20 looks cheaper at £2.20 per kg, but at 100 g a day half of it is left when it turns after five days, so you really pay £4.40 per kg of yogurt eaten.
Reading the result
The pack marked "cheaper for you" has the lower real price, and the monthly figure is what your usage costs with each. The break-even line says how much of the bulk pack you need to finish for it to pay off. Things that keep for months, such as rice or washing powder, usually favour bulk; fresh food and opened sauces often don't.
Questions
What should I enter for "keeps for"?
The shorter of two times: how long it lasts once opened (labels often say "use within 3 days of opening") and how long until its use-by or best-before date.
What if I freeze or share part of the bulk pack?
Then less is wasted. Raise "keeps for" to how long it lasts frozen, or enter only the part you keep as the bulk size and price, and the result updates.
Does it count storage space or extra trips?
No. It compares price and waste only. Freezer space, a heavier bag home or money tied up in a big pack are worth weighing yourself.