Time zone guides

Short explainers for anyone who works, travels or studies across time zones, written to answer the question and get out of your way. Every date and offset in them is worked out from the same time zone data that powers the rest of ClockDen.

Minutes to decimal hours Why 7 hours 45 minutes is 7.75 and not 7.45, how to convert minutes to decimal hours by hand or in Excel, and the timesheet mistakes that cost you pay. 5 min read How many time zones are there Why the answer is 24, 38 or 400+, which country has the most time zones, how many the US has, and where each new day begins. 5 min read How daylight saving time works Why clocks change, when they change in the US, UK and Australia this year, which countries skip it, and how to avoid missed meetings. 6 min read Best time to call India from the USA and UK Work out the best hours to call India from New York, Chicago, Los Angeles and London, in summer and winter, with a ready-made table. 6 min read Half-hour and 45-minute time zones Why India, Nepal, Iran and others are offset by 30 or 45 minutes from UTC, which places do it, and how to convert them without mistakes. 5 min read Why India has one time zone Why India uses a single time zone (IST, UTC+05:30), why it is a half hour offset, whether it has daylight saving, and what it means for scheduling. 5 min read UTC vs GMT explained What UTC and GMT are, how they differ, why computers and pilots use UTC, what a leap second is, and how to read offsets like UTC+5:30. 5 min read How time zones began How railways created time zones, why Greenwich became the world reference in 1884, and why zone borders are not straight lines. 4 min read IST to EST conversion India is 10h 30m ahead of EST and 9h 30m ahead of EDT. Learn how to convert in your head, with a quick table and common mistakes. 5 min read EST vs EDT, PST vs PDT The difference between EST and EDT, PST and PDT, when the US clocks change, and whether to write EST or ET in a message. 4 min read Scheduling across time zones A simple step-by-step way to schedule meetings across time zones, share the awkward hours fairly, and avoid daylight saving surprises. 5 min read How clocks stay accurate How atomic clocks and time servers keep the world on the same time, why a computer clock drifts, and how accurate an online clock is. 4 min read International Date Line What the International Date Line is, what happens when you cross it, why it zigzags, and where each new day and year begins first. 4 min read