What Is Daylight Saving Time and Why Does It Break Your International Calls?

Published 12 July 2026 · 8 min read

Twice a year, a routine that was working perfectly well stops working. The recurring Monday call that was 9am London / 5pm Singapore suddenly lands at 8am London / 5pm Singapore. Or the New York team shows up an hour late because they forgot the US clocks moved last Sunday but the UK's won't move for another two weeks.

Daylight saving time is the single most common cause of scheduling errors in global teams. Understanding exactly how it works — and which countries don't bother with it at all — is one of the most useful things a remote team manager can know.

What daylight saving time actually is

Daylight saving time (DST) is the practice of advancing clocks by one hour during summer months so that daylight lasts longer into the evening. The idea, first widely adopted in the early 20th century, was to reduce the need for artificial lighting and save energy. Whether it actually achieves that in the modern world is debated, but most of the US, Europe, Australia and New Zealand still observe it.

In practical terms: when a country moves to DST, clocks go forward by one hour ("spring forward"). Their UTC offset increases by one. When DST ends in autumn, clocks go back one hour ("fall back") and the UTC offset returns to its base value. A country that is normally UTC+0 becomes UTC+1 during DST. A country that is normally UTC+10 becomes UTC+11.

Countries that don't observe DST

Roughly 40% of countries do not observe DST at all. This group includes some of the world's most significant business hubs. Knowing which major cities have a stable year-round offset is genuinely useful for remote teams:

• India (IST, UTC+5:30) — never observes DST. The offset is always 5 hours 30 minutes ahead of UTC.
• China (CST, UTC+8) — the entire country uses a single time zone year-round, despite spanning five geographic zones.
• Japan (JST, UTC+9) — stable year-round, which makes it a reliable anchor for Asia-Pacific scheduling.
• Singapore (SGT, UTC+8) — no DST. Always 8 hours ahead of UTC.
• Most of Africa — the majority of African countries have stable offsets year-round.
• Most of Southeast Asia — Thailand, Indonesia, Vietnam, Malaysia and others do not observe DST.
• UAE and Saudi Arabia — Gulf countries do not use DST.

The implication: if you're scheduling between, say, London (which observes DST) and Singapore (which doesn't), the offset between them changes by one hour twice a year. A meeting that works perfectly in January might fall an hour outside someone's workday by April.

Why transitions don't happen on the same date everywhere

Even among countries that do observe DST, the transition dates are different. The US switches on the second Sunday in March and the first Sunday in November. The EU transitions on the last Sunday in March and the last Sunday in October. Australia and New Zealand, in the southern hemisphere, have summer in the opposite half of the year, so their transitions run roughly from October to April.

This misalignment creates a particularly confusing two-week window after each major transition. For example, after the US springs forward in mid-March but before Europe does in late March, the New York–London offset temporarily changes. A team that scheduled their calls based on a "5-hour gap" assumption will be off by one hour for approximately two weeks.

The southern hemisphere complication

Australia and New Zealand deserve special mention because their DST schedules are inverted relative to Europe and North America. When it's winter in London (October to March), it's summer in Sydney. When the UK is on GMT (no DST), Australia might be on AEDT (UTC+11 for New South Wales). When the UK moves to BST (UTC+1) in late March, Australia moves the other direction as its summer ends.

The result is that the Sydney–London offset oscillates between 9 and 11 hours across the year, depending on the DST status of both countries at any given moment. You can't safely assume a fixed gap.

Real-world examples of DST confusion

The most common DST scheduling mistake is running a recurring meeting on a fixed clock time without adjusting for transitions. If your weekly sync is set as "3pm London every Tuesday" in a calendar system that doesn't properly handle DST, the US participants might find it appearing as 10am or 11am Eastern depending on the time of year — not because anyone changed anything, but because the offset shifted.

A subtler version: two teams schedule a call by agreeing "let's say 10pm Singapore / 3pm London." Both are correct on the day they agree. But three months later, the UK has moved to BST (UTC+1). Singapore hasn't changed. Now the call is 10pm Singapore / 4pm London. Nobody updated the calendar invite. The Singapore person expects the London team to join at 3pm their time; the London team has it correctly in their calendar as 4pm. One side is an hour early, one is on time.

How to protect your schedule from DST surprises

A few practical things that make a material difference:

• Use a tool that recalculates on the specific date. Rather than noting a gap as "London is 8 hours behind Singapore," always verify the offset for the actual meeting date using a tool that applies current DST rules.
• Set a calendar reminder around transition dates. The major transition windows are late March, late October and (for the US) early November. A quick recurring reminder to review international meeting times after each transition will catch most problems before they cause missed calls.
• Don't just rely on calendar auto-conversion. Most modern calendar apps will handle time zone conversion correctly when you've set the event in a specific time zone — but only if the time zone is stored correctly, not just as a UTC offset. Events stored as "UTC+1" will not update when DST changes; events stored as "Europe/London" will.
• Watch for the DST warning on your planner. A good time zone tool will flag when any of your selected cities is within two weeks of a DST transition, prompting you to double-check before locking in a time.

DST rules are set by individual governments and can change with little notice. Several countries have proposed or enacted DST abolition in recent years. Always verify current rules for specific dates, particularly for upcoming transitions.