Pick a time and a set of zones to see them side by side, with a bar showing which hours fall in working time everywhere. Daylight saving is handled from your browser's own time zone database, so the answer stays right across the weeks when regions switch on different dates.
London is five hours ahead of New York — except for about three weeks a year. The US switches to daylight saving on the second Sunday in March and Europe on the last Sunday in the same month, and they switch back on different dates too. During those windows the gap is four hours. Anything that hard-codes "UTC-5" or "+5 hours" is wrong twice a year, every year. This tool reads your browser's IANA database, so the arithmetic follows the actual rules.
UTC is the atomic time standard that every zone is defined as an offset from. GMT is a time zone that equals UTC in winter and becomes UTC+1 during British Summer Time. For scheduling, say UTC.
"14:00 Europe/Berlin" is unambiguous all year round. "14:00 UTC+2" is only correct for part of it. Calendar software does this correctly; humans writing times into emails usually do not.
Not every offset is a whole hour. India is UTC+5:30, Nepal UTC+5:45, parts of Australia UTC+9:30, and the Chatham Islands UTC+12:45. Any code that stores offsets as integer hours breaks for about a fifth of the world's population.
Automatically, using your browser's IANA time zone database. This matters more than it sounds: the US and Europe switch on different dates, so for a couple of weeks each spring and autumn the gap between London and New York is four hours rather than five. Fixed offsets get this wrong every year.
UTC is the atomic time standard every zone is defined as an offset from. GMT is a time zone that happens to equal UTC in winter and shifts to UTC+1 during British Summer Time. For scheduling, say UTC and mean it.
Because offsets change twice a year but zone names do not. "14:00 Europe/Berlin" is unambiguous all year; "14:00 UTC+2" is only correct for part of it.
Steuervergleich Kanton Zürich — Gemeindesteuern vergleichen (Deutsch)