A project lead in Chicago sends a calendar invite for 3 PM to a developer in Berlin and a designer in Tokyo. The Berlin dev joins an hour late because the invite did not account for Europe’s earlier spring-forward date. The Tokyo designer shows up on time but it is 5 AM local — nobody checked whether the slot fell inside working hours on the other end. Scheduling across zones is not hard math, but time zone meeting planner mistakes almost always come from ignoring DST shifts or forgetting that “business hours” means different clock ranges in different cities.
Pick the zones you need, set each participant’s working window, and the tool highlights the overlap where everyone is available during reasonable hours. The result flags any zone where a DST change shifts the offset before your chosen date.
Finding the Overlap When “9 to 5” Means Three Different Clocks
New York and London are five hours apart most of the year but only four during the weeks between the US and UK clock changes. Add a third zone like IST (India, UTC+5:30) and the shared window shrinks fast. The planner lays every zone on a single 24-hour grid and shades the hours that land inside all working windows at once.
If the overlap is zero the grid makes that obvious — no shared band exists. In that case you either shift one person’s window (maybe someone takes an early or late slot) or split the meeting into two calls. Seeing the gap visually beats guessing with a spreadsheet.
DST Traps: Spring Gaps and Autumn Overlaps
Daylight saving creates two edge cases. In spring, clocks jump forward and one hour vanishes — 2:00 AM becomes 3:00 AM, so a meeting at 2:30 AM local does not exist. In autumn, clocks fall back and one hour repeats — 1:30 AM happens twice, making a calendar invite for that slot ambiguous without an offset label.
The bigger trap is that countries switch on different weekends. The US springs forward in early March while the EU waits until late March, creating a window where the usual New York-to-London offset drops from five hours to four. A recurring weekly meeting during that window will land an hour off on one side unless the invite is pinned to a specific UTC offset. The planner uses IANA identifiers (likeAmerica/New_York) which carry DST rules baked in, so the overlap grid shifts automatically when a clock change is in play.
City Names Beat Abbreviations — Here’s Why
“EST” is not a time zone — it is half of one. Eastern Time alternates between EST (UTC−5) in winter and EDT (UTC−4) in summer. Selecting America/New_York captures both halves and lets the planner know when the switch happens. The same goes for “BST” versusEurope/London, or “IST” which could mean India, Israel, or Ireland depending on context.
If a zone is missing from the dropdown, pick the nearest major city in the same region. IANA identifiers follow a Continent/City pattern, and two cities that share the same offset and DST schedule are interchangeable.
Scheduling Questions
- Best meeting time between New York and London? Most of the year the overlap sits between 9 AM ET and 1 PM ET (2–6 PM GMT). During the DST gap weeks in March it shifts by an hour.
- Does the planner update for DST automatically? Yes. It reads IANA zone data from your browser, so offsets adjust as clock-change dates pass.
- Can I add more than two zones? Add as many as you need. The overlap narrows with each zone, and the grid makes it clear when no shared window remains.
Related tools: Event Countdown Timer for a live ticker to your scheduled meeting, Business Days Calculator for working-day counts that skip weekends, Days Between Dates Calculator for calendar-day spans, and How Long Since / Until for elapsed time with hours and minutes.
Zone offsets rely on your browser’s IANA database. DST transitions follow the rules in that database and may not reflect last-minute government schedule changes.