How much does daylight saving change your client overlap?

One representative city per time zone, ranked by how much its overlap with a London working day changes between 15 January and 15 July 2027. A negative change means you lose shared hours in the British summer.

The three patterns

You do not change and Europe does. This is most of the tropics. Britain moves forward an hour in late March, you do not, so the gap between you widens by an hour and you lose an hour of overlap until late October. Accra goes from 8h to 7h. Annoying but predictable.

You do not change and America does. Same mechanism, opposite consequence, because the United States moves an hour earlier relative to you as well — but from a starting point that usually made you level rather than behind. Most of the Andes gains convenience here rather than losing it, which is covered on the New York overlap page.

You change in the opposite direction. Chile, Paraguay, Argentina’s neighbours, New Zealand and southeastern Australia all sit in the southern hemisphere. When Britain springs forward, they fall back. The two effects add rather than cancel, which is why Santiago swings two hours and everywhere else swings one.

The dates, which are not the same everywhere

The European Union and the United Kingdom change on the last Sunday in March and the last Sunday in October. The United States and Canada change on the second Sunday in March and the first Sunday in November. That leaves two gaps a year — about three weeks in March and one in late October — when the transatlantic difference is four hours instead of five, or six instead of five.

Those weeks are when standing meetings quietly move and nobody announces it. If you have a recurring call with both London and New York on it, the March gap is the one that breaks it, because for three weeks the two cities are only four hours apart and the slot that used to suit both no longer does.

Southern hemisphere dates are different again — Chile changes in early September and early April, New Zealand in late September and early April, Australia in early October and early April. None of these align with anything.

What to actually do about it

The practical answer is to put the two changeover dates that affect you into your calendar as all-day events, a year in advance, and to write recurring meetings in the client’s time zone rather than yours. Every serious calendar tool will do this; almost nobody turns it on.

The second practical answer is to check the July column before you sign a lease, not the January one. People choose a base in the northern winter, when the overlap happens to be at its best, and then discover in April that the arrangement they designed no longer fits. Ghana in January is London time. Ghana in July is not.

Countries that never move at all

Japan, South Korea, China, India, Singapore, Malaysia, Thailand, Vietnam, Indonesia, the Philippines, most of Africa, all of the Gulf, Iceland, Turkey, Russia, Argentina and Colombia hold a fixed offset all year. Living in one of these is genuinely simpler: your own clock never changes, and only your clients' relationship to you does.

Morocco is the odd one out worth naming. It holds UTC+1 permanently but steps back an hour for the month of Ramadan, which moves through the calendar by about eleven days a year. It is the only country on our list whose time zone follows a lunar calendar, and it catches out anyone who assumed 'no daylight saving' meant 'never changes'.