Common Availability Calculator

Everyone is free between the latest start and the earliest end

The time a whole group has in common is the stretch where every person's availability overlaps. For two people, it runs from whichever start comes later to whichever end comes first, and it exists only if that later start falls before the earlier end. Adding people changes nothing about the rule: you keep only the part that every single person has open.

In the first-screen “Team meeting” example, all four people are free on Monday from 10:30 AM – 11:30 AM and from 3:30 PM – 5:00 PM. In the morning Ava is free from 10:30 and Noah drops out at 11:30, which leaves one hour. In the afternoon Ava starts at 3:30 and Noah is free until 5:00, which leaves an hour and a half. On Tuesday and Wednesday there is no time when all four are free. In the option list, the two all-four windows come first, followed by three-person windows, and times without Mia, who is marked as required, never appear. Tuesday 11:00 AM – 12:00 PM (without Ava) and Wednesday 2:00 PM – 3:00 PM (without Noah) are listed after Monday's three-person options.

When it helps

• Sorting out replies in a group chat or email thread: answers like “Mon 9-12, Tue after 2” are scattered across Slack, iMessage or a long email chain. Type each one into that person's row and the overlap, plus who is left out, appears on one screen.
• Interview panels and anyone who has to be there: mark the hiring manager or the candidate as required, and every option without them disappears.
• Book clubs, study groups and weekly D&D or gaming nights: switch from dates to weekdays and the tool looks for a slot that repeats every week instead of one specific date.
• Late-night sessions and calls across time zones: type 10pm-2am in one cell and the calculator carries it past midnight into the next morning.

How the calculation works

1. Each cell is read as time ranges. When the end is earlier than the start, as in 22-2, the end falls on the next day.
2. A person's own ranges are merged first. 9-11 and 10:30-12 become 9:00 AM – 12:00 PM, and touching ranges such as 9-10 and 10-11 become 9:00 AM – 11:00 AM.
3. The day is cut at every start and end time anyone entered, and the free people in each piece are counted. The shade of a cell on the availability map is that count.
4. Candidates are the longest stretches in which the same set of people is free from beginning to end. Stretch a candidate earlier or later and someone inside it drops out; no one else is free throughout.
5. Candidates shorter than your minimum, and those missing a required person, are removed. The rest are sorted by how many people can come, then by earliest start.

Shared time = [latest start, earliest end) · only if latest start < earliest end · length = earliest end − latest start

Ranges include their start time but not their end time. So if one person is free until 10:00 and another from 10:00, they share 0 minutes. The W3C time ontology draws the same line: when the end of one interval coincides with the beginning of the next, it calls the relation “meets” and treats it as separate from overlapping.

How to type times

Each cell holds one person's free time for that day. Separate several ranges with commas. You can use am and pm, or a 24-hour clock. Below the cell, a bar and a length show exactly how your entry was read.

Three people, one day: the minimum length changes the options

Suppose that on the same day Mia is free 9:00 AM – 12:00 PM and 2:00 PM – 4:00 PM, Noah 10:00 AM – 11:00 AM and 2:30 PM – 5:00 PM, and Ava 10:30 AM – 1:00 PM and 3:00 PM – 4:30 PM. In the morning the latest start is Ava's 10:30 and the earliest end is Noah's 11:00, so all three share 30 minutes. In the afternoon Ava arrives at 3:00 and Mia leaves at 4:00, which gives one hour.

The minimum applies to one unbroken stretch. The tool never adds the morning's 30 minutes to the afternoon's hour to make a 1 hour 30 minute option. A stretch exactly as long as your minimum is kept.

If an option is long, you can start the meeting anywhere inside it as long as it finishes before the option ends. In the 3:00 PM – 4:00 PM option, a 30-minute meeting can begin at 3:00 or at 3:30. The calculator does not split the window into 30-minute booking slots, so factor in travel and prep time when you choose a real start.

When no one time works for everyone

With more than five people, there is often no time that suits everybody. Instead of an empty result, the calculator promotes the time when the most people can come to the top and names who is missing. In the people list above the result, anyone who cannot make it shows as an empty circle with a strikethrough.

The “Weekly study” example has five people and three weekday evenings: Monday, Wednesday and Thursday. No day suits all five, but on Thursday from 8:00 PM to 10:00 PM four people, everyone except Hannah, are free for two hours. Monday and Wednesday offer only one hour of four-person overlap, so they drop out once the minimum is 1 hour 30 minutes. Try it

If the result isn't good enough, loosen the conditions in this order:

1. Keep only the people who must be there. Mark them as required. Options without them vanish, and the best remaining option for everyone else comes first.
2. Lower the minimum length. You will see right away whether everyone shares even a short stretch. Dark cells with a ✓ on the map are the moments when all are free.
3. Add days. More candidate dates mean more chances to overlap. Removing a date does not erase the times you entered; add it back and they return.
4. Split the meeting. Pick two time slots with different shading on the map and run the same session twice.

Calendar software solves a related problem. The iCalendar standard (RFC 5545) defines a FREEBUSY property that carries only free or busy intervals instead of full events, and Outlook's Scheduling Assistant has you add attendees as Required or Optional. This calculator does not connect to any calendar; it does the same overlap math using only the availability people give you.

Past midnight, and repeating weekdays

Someone free from 10 PM to 2 AM types 10pm-2am once, in that day's cell. The calculator treats it as a four-hour stretch that continues until 2:00 AM the next day, and it counts overlap with others who are free in the early hours of that next day. The map's time scale runs past midnight (24, then 1, 2), so the part after midnight continues at the bottom of the same day's column; when the map shows the whole day, it is drawn at the top of the next day's column instead. In each person's cell bar, the next-morning part is hatched.

In the “Late night” example all four people are free on Friday from 10:00 PM to 11:30 PM, but that is only 1 hour 30 minutes, so with a 2-hour minimum it is not an option. The first option is then 9:00 PM – 11:30 PM with three people, missing Leah. Lower the minimum to 1 hour 30 minutes and the all-four window, 10:00 PM – 11:30 PM, comes first. Try it

“Weekdays” compares recurring days of the week rather than particular dates. Use it for a standing meeting that repeats every week, and switch back to dates if someone is free only this week. Times for dates and for weekdays are stored separately, so switching between them erases nothing.

Bringing in a spreadsheet at once

If you collected availability in a form or a spreadsheet, importing a file is faster than typing. Put one range for one person on each row; rows with exactly the same name are treated as one person. “Download Excel” saves what you have entered in the same layout, so you can also use that file as a template.

What Excel shows in a cell and what it stores can differ. Excel stores dates as serial numbers and times as fractions of a day, so 12:00 PM is 0.5. The calculator reads dates and times stored as numbers, and it corrects files made with the 1904 date system, whose serial numbers run 1,462 days lower. Still, after importing, check that the number of people and the dates and times match your source. Values like 10/5 with no year, or a bare 3 with no am or pm, may be unreadable or read differently than you meant.

Common mistakes

• Typing an afternoon time like a morning one: 2-4 means 2:00 AM to 4:00 AM. For the afternoon, write 2-4pm or 14-16. If the bar under the cell sits against the far left edge, suspect this.
• Treating touching times as shared: someone free until 10:00 and someone free from 10:00 have no time together. A single person's 9-10 and 10-11, though, are joined into 9:00 AM – 11:00 AM.
• Spelling the same person two ways: in a spreadsheet, “Sam Lee”, “Sam Lee ” with a trailing space and “Sam” are not all the same. Extra spaces at the ends are trimmed, but other differences are kept, so they count as different people.
• Mixing people who haven't answered with people who can't make any day: a person whose cells are all blank is treated as not answered yet and left out of the calculation; their chip shows “no times entered, left out”. Someone who cannot make any day must type x (or “no”, “none”) in the cells to be counted in “everyone”. A single blank cell still means unavailable that day.
• Mixing time zones: if you type a remote guest's local times as they sent them, unrelated hours will overlap. Convert everyone to a single time zone first.

Limits and cautions

• No time-zone conversion. Every cell is treated as a time in the same zone, and the skipped or repeated hour when daylight saving time changes is not handled.
• Up to 20 people and 14 candidate dates. The on-screen list and the copied result show at most 12 options.
• In weekdays mode, a stretch that starts on Sunday night and runs into early Monday is not joined to Monday of the same week.
• What you type stays in this browser and is not stored on a server. The link you copy contains names and times, so shorten the names before posting it somewhere public.
• If several people open their own copies of a link and edit at the same time, only the last link posted survives. The most reliable approach is for one person to collect the replies and enter them.

Checked on October 23, 2026. Excel's date and time storage was checked against Microsoft Support, the definition of touching intervals against the W3C time ontology, and the free/busy notation against RFC 5545.

Sources

• 01Microsoft Support: Date systems in ExcelThe 1900 and 1904 date systems, and the 1,462-day difference between their serial numbers
• 02Microsoft Support: TIME functionTime values are decimal fractions of a day; 12:00 PM = 0.5
• 03RFC 5545 iCalendar, 3.8.2.6 Free/Busy TimeFREEBUSY defines one or more free or busy time intervals (FBTYPE FREE, BUSY and others)
• 04W3C Time Ontology in OWL, 4.2.30 intervalMeetsThe relation where the end of one interval coincides with the beginning of another (“meets”)
• 05Microsoft Support: Scheduling Assistant in OutlookMeeting attendees go in separate Required and Optional fields

Frequently asked questions

Related tools