Time zone converters

Each comparison is anchored to one city's day. The 24-hour table starts at midnight in the first city named in the title and walks through its day an hour at a time; every row shows what the clock says in the second city at that same instant. When the second city has already turned the page on the calendar, the row is marked as the next day or the previous one.

That anchoring is why each direction gets its own page instead of one page with a swap button. The hours worth knowing about differ depending on which end of the call you are sitting at: "when can I reach them from here" has a different answer from "when will they be reaching me".

The last column of the table answers one question — can both sides actually take the call? It reads as a yes only when the hour falls inside a working day of 09:00–17:00 local time on both sides. When one city is at work and the other is not, it says so, and when neither is, the hour is marked as outside hours. Above the table, the same information is collapsed into windows: the unbroken runs of shared hours, each given in both cities' local time.

Some pairs have no shared hours at all, and those pages say so rather than proposing a compromise nobody asked for. That is the case for 14 of the 57 comparisons listed here.

All of it is computed when the site is built, so the tables are already in the HTML and work with JavaScript switched off. The only part that needs a script is the line giving the current time in each city, which by definition cannot be static.

A city's offset from UTC is a political decision rather than a fact of geography, and it is not necessarily a single number. Of the 31 time zones behind the 36 cities on this site, 16 shift their clocks at some point in 2026 and 15 hold one offset all year. The gap between two cities is the difference between two of those offsets, so it only stays put while both sides are on the same setting — and often they are not.

Daylight saving does not change a zone's standard offset. It changes which of two offsets is in force: the clocks go forward, usually by an hour, on a date each country picks for itself, and come back later in the year. Two countries that both observe it can still disagree for weeks, simply because they picked different dates.

New York and London are the clearest case on this site. New York moves its clocks first, on 8 March 2026, and London does not follow until 29 March 2026. For those 21 days London is 4 hours ahead of New York rather than the 5 hours ahead it is through the middle of the year. In autumn the same thing happens in the opposite order: London falls back on 25 October 2026, New York not until 1 November 2026, and there are 7 more days at 4 hours ahead. A recurring meeting booked across either boundary drifts by an hour without anyone touching it.

South of the equator the order is reversed: Sydney and Auckland put their clocks back in the first half of the year and forward again in the second, because their summer is the northern winter. Pair one of them with a northern city that also shifts and the two movements add up instead of cancelling: across 2026 the gap between London and Sydney runs from 9 hours ahead to 11 hours ahead — a swing of 2 hours rather than one.

The zones that never move are not the easy case either. Phoenix, Bogotá, Mexico City and São Paulo hold one offset all year, so a gap involving them changes whenever the other side moves, and only then. Two of those are recent: Mexico abolished daylight saving in 2022 and Brazil suspended it in 2019, which invalidated a great deal of published material overnight.

This is why no page here states one number for the difference between two cities. Each splits the year into the stretches where the gap genuinely is constant and describes them separately — 43 of the 57 comparisons above need more than one stretch in 2026. Picking a single number instead is wrong for several weeks a year, and wrong without announcing itself.