How long will it last? Count the days, the last day, and how much to get

How the page counts

• Amounts can have parts. The page counts in hundredths, so half of one (0.5) and 2.25 are exact.
• How long it lasts: how much you have, divided by how much gets used each day or each week. Only full days or weeks are counted, and the page shows what is left over.
• The first day is day 1. Something that lasts 15 days from a Monday has its last day on a Monday two weeks later, not on the Tuesday.
• With days ahead: the page counts back that many days from the last day. It is a day on the calendar, not a reminder.
• How much is needed: how much gets used each day or each week, times the number of days or weeks.
• Packs: what is needed, divided by how many come in one pack. A part of a pack counts as one more pack, and the page shows what is left over.
• The page only multiplies, divides and counts days. It uses the numbers you type and nothing else.

Examples, worked by hand.

• You have 30 and 2 get used each day: 30 ÷ 2 = 15 full days, with none left over. If the first day is Monday, October 12, 2026, the last full day is Monday, October 26, 2026, and on Tuesday, October 27, 2026 there is none left. 5 days before that last day is Wednesday, October 21, 2026.
• You have 100 and 8 get used each day: 12 days is 96, and 13 days would be 104, so it lasts 12 full days, and 4 are left over.
• You have 30 and half of one (0.5) gets used each day: 30 ÷ 0.5 = 60 full days.
• You have 20 and 3 get used each week: 6 weeks is 18, so it lasts 6 full weeks, and 2 are left over. 6 weeks is 42 days. If the first week starts on Monday, October 12, 2026, the last full week ends on Sunday, November 22, 2026.
• 2 each day for 30 days: 2 × 30 = 60. If 28 come in one pack, 2 packs is 56, which is not enough, so it takes 3 packs. 3 packs is 84, and 24 are left over.

The examples are made up. A program checks them, and 400 made-up counts done a second way, every time the page is built.

Where these counts trip people up

• What is left over is not a day. 100 at 8 each day is 12 full days with 4 left over, not 13 days.
• The first day counts. 15 days that start on Monday, October 12 end on Monday, October 26, not on Tuesday the 27th.
• 30 days is not always a month. 30 days that start on Friday, January 1, 2027 end on Saturday, January 30. January has 31 days, so the last day of the month is not covered.
• Packs go up to the next whole one. When 60 are needed and 28 come in a pack, 2 packs is 56. It takes 3.
• Counting by weeks counts only full weeks. 30 at 14 each week is 2 full weeks with 2 left over. The same 30 at 2 each day is 15 full days.

What this page does not know

• It does not know how much anyone needs to use or take. For a medicine, the label and the person who prescribed it say that. This page never does, and it never suggests using less to make something last.
• It does not know the days that differ: a spill, a lost one, a guest, a baby who is growing.
• It does not know when a pharmacy can refill, what an insurance plan allows, how long shipping takes, or whether a store is open on a weekend or a holiday.
• It does not know use-by dates, or how long something keeps once it is opened.
• It does not know prices. Unit price is the page for comparing two sizes.
• It will not remind you of anything. It names a day; Dates to keep is a place to write it down.
• It holds up to 20 counts on this device, and they do not move to another phone or computer by themselves.

If something is about to run out

• For a medicine: the pharmacy, or the office that prescribed it, is who to call. They can say what can be done, and this page cannot.
• For food: When you need food lists places to turn. For diapers, formula and other supplies, calling 211 reaches a local helpline in most of the U.S. that knows what help is near you.
• When money is the reason: Help with money.