Time Difference Calculator
Compare the local time in 2–5 cities at once. Live ticking clocks, DST status, day-of-week labels, exact difference in hours and half-hours — and a working-hours overlap chart that plots every city on a single UTC axis so you can see at a glance when everyone is simultaneously at their desk.
The meeting-overlap visualization — the killer feature most tools miss
Most "time difference calculator" tools online give you the difference in hours and nothing else. That is fine for a quick sanity check ("Tokyo is 13 hours ahead of New York, got it"). It does not help when you are trying to schedule a meeting across four time zones and you cannot mentally hold the UTC offsets in your head.
The bar visualization at the top of the result panel translates each city’s working hours into a band on a single shared 24-hour UTC axis. Where every band overlaps, every city is simultaneously in working hours — and that is the meeting window. Drag the working-hours setting (default 9–17) and watch the green overlap zone grow or shrink.
For four-city teams (NY-London-Bangalore-Singapore) the overlap is famously about 30 minutes a day. The visualization makes it instantly visible which30 minutes — and whether shifting one city’s working hours by an hour would expand it. We have not found another free time-difference tool that does this.
How to use the time difference calculator
Five steps. The defaults already work for the most common case (NY ↔ London).
- Pick your cities. Two cities are loaded by default (New York and London). Tap a quick-pill (Tokyo, Paris, Sydney, Dubai, Mumbai, Singapore, São Paulo, Berlin, LA, UTC) to add it instantly, or use "Add a city" to search anywhere worldwide. Up to five cities at once.
- Read the live clocks. Each city card shows the local time as a big ticking clock (HH:MM:SS), the date and weekday, the IANA timezone, the UTC offset, and the timezone abbreviation (EST/EDT, GMT/BST, JST, etc.). DST status — "DST in effect" or "Standard time" — is shown as a small coloured pill.
- Read the time difference. The first city in your list is the "primary". Every other city shows its offset from the primary in hours and half-hours (+5h, -3h 30m, +13h). This is the actual current difference, accounting for DST in both locations.
- Find a meeting overlap. Set the working-hours range (default 9 to 17 in each city’s local time). The "Working-hours overlap" card plots every city’s working hours on a single UTC axis; where the bands overlap, every city is simultaneously in working hours. The numerical readout shows the overlap window and total hours.
- Translate a specific time. Use the date/time picker at the top to set a specific moment at the primary city — useful for "Monday 10am NYC, what time is that for everyone else?" The clocks freeze at that moment. Tap "Now" to return to the live clock.
What people use this tool for
Seven recurring patterns we see in the analytics.
Scheduling cross-time-zone meetings
Pick the cities your meeting participants are in. Set the working-hours range. The overlap card highlights when everyone is at their desk simultaneously. Send the meeting invite at any time inside the overlap zone — no one has to wake up at 4am or stay late. Particularly useful for global teams (NY-London-Bangalore-Singapore-Sydney is famously a four-hour overlap challenge).
Booking international calls and consulting
Freelancers and consultants serving clients in different time zones use this as the first thing they open before sending a Calendly link. The dual clock shows you immediately what time it would be at your client when you propose a slot — so you do not accidentally ask a Tokyo client for "10am my time" which is 3am theirs.
Travel preparation and jet-lag planning
Before a trip, set your home city + destination city. The time-bar visualization shows you where the day-cycles align and how big the jump is. Use the picker to "set arrival time" and see what time it will be back home — useful for letting family/work know when to call.
Live event watching across time zones
Sports finals, product launches, awards shows — set the event city + your city, set the event time using the picker, and the tool shows you the local time you need to tune in. The day-of-week label (Monday vs Tuesday) catches the trickiest cases where the event spans midnight in one zone.
Coordinating around DST transitions
Twice a year, time zones in the US, EU, Australia, and a few other countries shift by an hour. Most other countries do not. The result: the time difference between, say, NY and London changes during the two-week gap when one country has switched and the other has not. The tool shows live DST status; if "DST in effect" badges differ between your cities, that is exactly when this confusion happens.
Cross-zone customer support and on-call rotations
Engineering on-call schedules across continents need a clear picture of who is available when. Set 4–5 cities and look at the bar: at any UTC hour, you can see which cities have someone in working hours. Helps build hand-off schedules and identify "dead zones" where no one is awake.
Family and friends spread across the world
When is a good time to call my parents in Karachi? My friend in Vancouver? My sibling in Cape Town? Add their cities, glance at the overlap. The DST badges flag the half-year edge cases. Saves the "wait, what time is it there now?" mental math every time.
Time differences between common city pairs
Quick reference table for the most-searched city pairs. The "diff" column shows the current standard difference and any DST-driven variations. Use the tool above for the live-accurate value at this exact moment.
| Pair | Difference | Note |
|---|---|---|
| New York ↔ London | 5 hours (NY behind London) | During DST gap (mid-March to early April; late October to early November) the difference is 4 hours. |
| New York ↔ Los Angeles | 3 hours (LA behind NY) | Both observe DST simultaneously; difference is constant year-round. |
| New York ↔ Tokyo | 13 hours (Tokyo ahead) Std / 14 hours during NY DST | Tokyo does not observe DST; New York does. Difference shifts an hour twice a year. |
| New York ↔ Sydney | 14–16 hours (Sydney ahead) | Both observe DST but offset by 6 months (Southern hemisphere). Maximum difference 16 hours during NY winter + Sydney summer. |
| London ↔ Singapore | 7 hours (Singapore ahead) Std / 8 hours during BST | Singapore does not observe DST; London does. Standard 8 hours during British Summer Time, 7 hours otherwise. |
| London ↔ Mumbai | 4.5 hours (Mumbai ahead) Std / 5.5 hours during BST | India Standard Time is +05:30 — note the half-hour offset. |
| London ↔ New Delhi | 4.5 / 5.5 hours | Same as Mumbai (India is single time zone). |
| San Francisco ↔ Tokyo | 16 / 17 hours (Tokyo ahead) | Tokyo does not observe DST; SF does. 16 standard hours, 17 during PDT. |
| Sydney ↔ London | 9–11 hours (Sydney ahead) | Both observe DST in opposite seasons. Maximum 11 hours during Sydney summer + London winter. |
| Dubai ↔ New York | 8–9 hours (Dubai ahead) | Dubai does not observe DST; NY does. 9 hours standard, 8 during EDT. |
How the tool actually works
1. Time-zone data
We use the IANA Time Zone Database — also known as the tz database, the Olson database, or zoneinfo. It is the universally accepted source of time-zone data: Apple, Google, Microsoft, Amazon, every major Linux distribution, and the standard libraries of Python, JavaScript, Ruby, Go, etc., all use it. The IANA database tracks UTC offsets, DST rules, and every historical transition for every named timezone since 1970, and it is updated several times a year as countries change their rules.
2. Browser Intl API
The math runs in your browser via Intl.DateTimeFormat, which is backed by the IANA database that ships with your operating system. We call it once per second per city to format the local time. No data leaves your browser; the only network call is the initial timezone lookup when you add a custom city.
3. Coordinate-to-timezone resolution
When you add a custom city via search, we hit our /api/timezone endpoint, which uses the geo-tz library — a server-side polygon-based resolver that maps any (latitude, longitude) to the correct IANA timezone string. geo-tz handles edge cases like sub-state timezone boundaries (e.g., Indiana, where some counties are on Eastern Time and others Central).
4. DST detection
We compute the UTC offset at January 15 and July 15 of the current year. If the two offsets differ, the city observes DST. To detect whether DST is currently in effect, we compare today’s offset to the smaller of the two — if today’s is greater (clock has moved forward), DST is on. The "DST in effect" pill turns yellow during DST and grey during standard time.
5. Working-hours overlap
For each city, we convert the working-hours range from local time to UTC by subtracting the city’s UTC offset (with DST applied). If the converted range wraps past midnight UTC, we split it into two segments. Then we compute the geometric intersection of all cities’ segments. The result is the UTC-axis window during which every city is simultaneously in working hours.
SimpleMapLab vs other time-difference calculators
Honest comparison. Each tool wins different scenarios — this is a feature checklist, not a value judgement.
| Feature | SimpleMapLab | timeanddate.com | worldtimebuddy | worldtimeserver.com | Time Zone APIs |
|---|---|---|---|---|---|
| Free, no sign-up | ✓ | ✓ | ✓ | ✓ | Limited / paid |
| Live ticking clock per city | ✓ | ✓ | Limited | ✓ | API only |
| Working-hours overlap on UTC axis | ✓ | ✗ | ✗ | ✗ | ✗ |
| Multi-city (up to 5) | ✓ | Up to 4 | Up to 6 | Pairs only | ✓ |
| DST status badge per city | ✓ | Limited | Limited | ✓ | Limited |
| IANA timezone label + abbreviation | ✓ | Limited | Limited | Limited | ✓ (paid) |
| Date / day-of-week awareness | ✓ | ✓ | Limited | ✓ | ✓ |
| Set custom reference time | ✓ | ✓ | ✓ | ✓ | ✗ |
| 12h / 24h toggle | ✓ | ✓ | Limited | ✓ | ✗ |
| Sub-day half-hour offsets (India, Iran, etc.) | ✓ | ✓ | ✓ | ✓ | ✓ (paid) |
| Mobile-first interface | ✓ | Partial | Partial | Partial | ✗ |
| No watermark, no rate limit | ✓ | Heavy ads | Heavy ads | Some ads | API key required |
Daylight Saving Time rules around the world
Roughly 70 countries observe DST, but they switch on different dates. Here are the current rules (subject to change — countries occasionally abolish or reinstate DST).
United States, Canada, and Mexico
Spring forward: second Sunday of March (2:00 local time). Fall back: first Sunday of November (2:00 local time). Exceptions: Hawaii and most of Arizona within the US do not observe DST. Mexico abolished most DST in 2022 — only the border states near the US still observe it.
Europe (Brussels Time / GMT+0 zones)
Spring forward: last Sunday of March (1:00 UTC). Fall back: last Sunday of October (1:00 UTC). All EU countries plus the UK, Iceland-no-actually-Iceland-doesn’t-observe-DST, and a few non-EU European countries follow these dates. The 2-week mismatch between US and EU DST in March/early November and late October/early November is the cause of the 4-hour-difference confusion between NYC and London.
Australia and New Zealand
Southern hemisphere — opposite seasons. Spring forward: first Sunday of October. Fall back: first Sunday of April. NSW, ACT, Victoria, South Australia, Tasmania observe DST; Queensland, Northern Territory, Western Australia do not. New Zealand observes DST nationally.
Most of Asia, Africa, and South America
Do not observe DST. Notable: Japan, China, India, Singapore, Hong Kong, Thailand, Vietnam, the entire continent of Africa, most of South America (Brazil and Chile abolished DST in 2019). When you compare a US/EU city with one of these, the offset between you shifts by an hour twice a year.
The half-hour and quarter-hour offsets — the gotchas
Most time zones are whole-hour offsets from UTC. Some are not:
- India (IST) — UTC+05:30. The whole country is one timezone.
- Sri Lanka — UTC+05:30. Same as India.
- Iran (IRST) — UTC+03:30. Iran also observes DST until 2022; abolished from 2023.
- Afghanistan — UTC+04:30.
- Newfoundland (Canada) — UTC-03:30. The only sub-hour timezone in North America.
- Myanmar (MMT) — UTC+06:30.
- Marquesas Islands (French Polynesia) — UTC-09:30.
- Nepal (NPT) — UTC+05:45. The only quarter-hour offset in routine use.
- Chatham Islands (NZ) — UTC+12:45 (with DST: +13:45).
The tool handles all of these correctly. The difference column shows fractional hours (e.g., "+5h 30m" or "+5.5h" or "-3h 30m") rather than rounding.
Related tools and resources
For the time zone of a single point: Time Zone Finder. For the country at any point: What Country Am I In?. For the bearing between two cities (after you pick a meeting): Bearing & Compass Calculator. For the geographic midpoint between meeting participants: Halfway Between Two Places. For a random city to add: Random Location Generator. For sunrise/sunset at any city: Sunrise & Sunset Calculator.
Frequently asked questions
Time-zone data: IANA Time Zone Database(zoneinfo / tz / Olson) via the browser’s Intl.DateTimeFormat API. Coordinate-to-timezone resolution: geo-tz (BSD-licensed, OpenStreetMap-based polygon dataset), called via our /api/timezoneendpoint. DST detection: compare UTC offsets at January and July of the current year (different = observes DST), then compare current offset to the standard offset (greater = currently in DST). Working-hours overlap: convert each city’s 9-17 (or configured) range to UTC, split at midnight if needed, intersect across all cities. Country flags: rendered client-side from ISO 3166-1 alpha-2 codes via Unicode regional indicator codepoints. Live tick: 1 Hz client interval; no server polling. All math runs entirely in your browser; no data leaves the page beyond the optional add-city geocoding query.
More SimpleMapLab tools
Find the time zone of any location. DST detection and current local time.
Sunrise, sunset, twilight, golden hour, and day length for any location.
Identify the country at any GPS, address, or map click.
Compass bearing between two cities — true and magnetic.