Time Zone Meeting Overlap Calculator

Fit {{ summaryFit }} Duration {{ meeting_length }} min Zones {{ participantCountDisplay }}

Availability band unavailable

Team preset:

Presets cover common remote-team corridors without locking the roster.

Participant roster:

Format: Name | IANA timezone | HH:MM | HH:MM | optional weight. Use 2-10 rows.

Planning date:

Use a date from 2020 through 2035 so the shipped civil-time rule snapshot remains in range.

Reference timezone:

Choose the scheduler's zone or UTC for a neutral view.

Meeting length:

From 15 minutes to 8 hours.

minutes

Scan window:

A wider scan can find a better weekday without changing anyone's hours.

Recommendation mode:

Strict-first falls back only when no complete shared work-hour slot exists.

Candidate step:

The neutral default is 30 minutes.

Edge-hours buffer:

{{ edge_buffer }} min

The neutral default is 0 minutes; increase it only when early or late fallbacks are acceptable.

Workday rule:

The default keeps local weekends out of the shortlist.

Minimum fallback score:

The default 50-point threshold removes severe compromises.

/ 100

Calendar title:

The neutral default is Team meeting.

Calendar location:

Leave blank when the organizer will add the location later.

Rank	Reference start	UTC start	Score	Fit	Copy
{{ row.rank }}	{{ row.reference_start }}	{{ row.utc_start }}	{{ row.score_display }}	{{ row.fit }}

Workday fit map unavailable

Participant	Local meeting	Work window	Fit	Local note	Copy
{{ row.name }}	{{ row.local_meeting }}	{{ row.work_window }}	{{ row.fit }}	{{ row.note }}

{{ calendarSummary }}

A workable international meeting is an interval, not a single clock reading. Its beginning and end must both fit each participant's local availability. A 60-minute call starting at 17:00 does not fit a workday that ends at 17:30, even though the start appears acceptable.

Civil time: The local date and clock time observed in a named region such as America/New_York.
UTC instant: The shared point in time used to compare every participant without local-clock ambiguity.
Work-hour overlap: A candidate whose entire duration stays inside every selected local work window.

Named IANA time zones are safer than abbreviations. CST, for example, can refer to different offsets, while a location-based identifier carries the regional daylight-saving rule. Even named-zone rules can change after governments revise civil time, so scheduling data needs a known date and a current source.

Sometimes no candidate fits everyone. A fallback then becomes a fairness decision: how many minutes fall before or after each person's stated hours, whose inconvenience carries more weight, and whether local weekends are allowed. A weighted score can rank compromises, but it should never hide the participant-by-participant local times.

Recurring meetings need another check. Daylight-saving transitions do not occur on the same dates everywhere, so an apparently stable corridor can shift by an hour for several weeks. Recalculate representative dates across the recurrence and rotate inconvenient times when one region repeatedly absorbs the burden.

How to Use This Tool:

Build the roster first, then decide how strictly candidates must respect the entered local hours.

Enter 2 to 10 participant rows as Name | IANA timezone | HH:MM | HH:MM | optional weight. Use an overnight pair such as 22:00 | 06:00 when the work window crosses midnight.
Choose a Planning date from 2020 through 2035, a Reference timezone, and a meeting length from 15 to 480 minutes.
Select a 1, 3, 5, or 7 day scan and a 15, 30, or 60 minute Candidate step. A smaller step tests more start times; a wider scan tests more dates.
Use Strict work-hours only when every participant must fit. Use Strict first, then fallback to prefer complete overlap, or Least-pain ranking to rank every candidate that meets the minimum score.
Review the first Best windows row against Participant impact. If no window qualifies, lower the fallback threshold, add an edge-hours buffer, widen the scan, or revise the roster rather than assuming the dates are unavailable.

Interpreting Results:

Full work-hour overlap means every minute of the meeting stays inside every participant's entered work window on an allowed local day. Equality at the start or end boundary is accepted. A candidate ending exactly at 17:00 therefore fits a window that ends at 17:00.

A Fallback is not equivalent to full overlap. Read the weighted score with Maximum pain and each participant's local meeting time. A high average can still conceal a poor result for a lightly weighted participant.

The shortlist is sampled at the selected candidate step. A 60-minute step can miss a valid start at 09:30, while a 15-minute step searches it. Before sending an invitation, verify the chosen date and local times in the calendar systems used by the participants.

Technical Details:

Each reference-zone candidate is converted to a UTC start and end, then projected into every participant's civil time. Evaluation uses the whole meeting interval, supports work windows that cross midnight, and can exclude local Saturdays and Sundays. Nonexistent reference times during a forward clock change are skipped.

Transformation Core

Meeting candidate transformation stages
Stage	Operation	Result
Candidate generation	Walk each selected date in the reference zone at the chosen step	UTC start and end instants
Local projection	Apply the supported zone's offset and civil-time rule to both ends	One local interval per participant
Fit evaluation	Compare the complete local interval with work hours, edge buffer, and workday rule	Strict, edge-hours, outside-hours, or weekend fit
Selection	Apply recommendation mode and minimum fallback score	Up to eight ranked windows

Formula Core

Each participant receives a fit score s_i and optional weight w_i. The candidate score is the weighted mean, rounded to one decimal place:

S = \frac{\sum_{i = 1}^{n} w_{i} s_{i}}{\sum_{i = 1}^{n} w_{i}}

Weights accept 0.25 through 3. They change the average only; they do not change any participant's displayed local time or the maximum minutes outside work.

Rule Core

The score bands are a planning heuristic rather than a scheduling standard.

Participant meeting fit scoring rules
Participant fit	Score	Boundary rule
Strict work hours	100	Local start ≥ work start and local end ≤ work end on an allowed day
Inside edge buffer	45 to 88	Whole interval stays inside the work window expanded by a positive buffer
Outside buffer on a workday	0 to 42	Penalty grows with minutes before or after the allowed window
Excluded local weekend	0	Applies when the Monday-Friday rule is selected

Strict work-hours only keeps strict candidates. Strict first, then fallback uses strict candidates whenever any exist and otherwise uses candidates at or above the minimum score. Least-pain ranking uses all candidates at or above that threshold. Candidates sort by strict status, higher weighted score, lower maximum pain, and finally earlier UTC start.

Accuracy Notes:

The scheduler supports a fixed list of 24 zone identifiers and a shipped civil-time rule snapshot for dates from 2020 through 2035. It is not a live copy of the IANA database, and a government change can make a future offset stale.

Use full location-based zone names rather than abbreviations or manually guessed UTC offsets.
Recheck future and recurring invitations in an up-to-date calendar, especially near daylight-saving transitions.
Treat weights and fallback scores as planning preferences, not proof that a meeting is acceptable to every participant.

Worked Examples:

The transatlantic daylight-saving gap

On 17 March 2026, New York has moved to daylight time while London has not. With both participants available from 09:00 to 17:00, a 60-minute meeting at 09:00 New York time appears as 13:00 in London and earns a strict score of 100. Repeating the same clock choice after the United Kingdom changes clocks shifts London's local time, which is why a recurring series needs another date check.

References:

Time zone and daylight-saving time data, Internet Assigned Numbers Authority.