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Time zones
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🌏 Every place has an offset from UTC (like +10 or −5). One rule runs everything: East = add, West = subtract. For flights, convert through UTC.

What it is

The world is split into time zones based on how far east or west you are. Each one has an offset from UTC (Coordinated Universal Time), the world's reference clock. Australia is ahead of UTC (UTC+10), the USA is behind (UTC−5). Converting between zones is just adding or subtracting the difference.

The one rule

East = add   ·   West = subtract

A higher UTC offset means further east, which means a later time. To compare two cities: find the difference in their offsets, then add if your target is east, subtract if west.

For a flight: convert the departure time to UTC, add the flight duration, then convert to the destination's local time.

Worked example

It is 18:00 in Brisbane (UTC+10). What time is it in London (UTC+0)?

  1. Offsets: Brisbane +10, London +0.
  2. Difference = 10 − 0 = 10 hours.
  3. London is west of Brisbane → subtract: 18:00 − 10 = 08:00.

Watch out

• Going past midnight or before 00:00 changes the day, add or subtract a day too.
• Use the offset the question gives, Sydney is UTC+10 in winter but UTC+11 in summer (daylight saving). Brisbane stays UTC+10.
• For flights, add the duration in UTC, not in local time.
• Some zones are half-hours (Adelaide UTC+9:30).

UTC in the middle, the world either side

⬅ WEST (subtract) EAST (add) ➡ New York−5 London (UTC)0 Brisbane+10

London is the reference (0). Go east (right) and you add hours, go west (left) and you subtract. Brisbane is 15 hours ahead of New York.

The flight method

  1. Departure → UTC (subtract the origin's offset).
  2. UTC + flight duration.
  3. UTC → destination (add its offset).

e.g. Brisbane 14:00 → 04:00 UTC, +9 hrs = 13:00 UTC, +9 (Tokyo) = 22:00 landing.

Warm up first

Don't read yet, just have a go in your head:

Going east, do you add or subtract?
Add. East is ahead, so a later time.
London 10:00 → Tokyo (UTC+9)?
Tokyo is east → add 9: 10:00 + 9 = 19:00.
Difference between UTC+10 and UTC−5?
10 − (−5) = 15 hours.

Faded example: comparing cities

Rung 1 · watch one done fully

18:00 Brisbane (+10) → London (0): diff 10, London is west → subtract: 18:00 − 10 = 08:00.

Rung 2 · you fill the gaps

07:00 New York (−5) → Brisbane (+10): diff = 10 − (−5) = ?, Brisbane is east → add: 07:00 + ? = ?

Check my gaps
15 hours, so 07:00 + 15 = 22:00 in Brisbane.
Rung 3 · all you (flight)

A flight departs London (UTC+0) at 06:00 and takes 6 hours, landing in Dubai (UTC+4). Find the local arrival time. Check below.

Check my answer
06:00 is already UTC. Add the flight: 06:00 + 6 = 12:00 UTC. Convert to Dubai (+4): 12:00 + 4 = 16:00 Dubai time.

Exam-style stretch: flight with a day change

A flight departs Brisbane (UTC+10) at 14:00 and takes 9 hours. What is the local arrival time in Tokyo (UTC+9)?

Show the working
Departure to UTC: 14:00 − 10 = 04:00 UTC. Add flight: 04:00 + 9 = 13:00 UTC. Convert to Tokyo (+9): 13:00 + 9 = 22:00 Tokyo time (same day).

Say it back

In one sentence, out loud: do you add or subtract when the target city is east?

⚡ Time zones, one look

UTCthe world's reference clock (offset 0)
Offsethours ahead (+) or behind (−) UTC
The ruleEast = add · West = subtract
Compare citiesdifference in offsets, then add/subtract
Flights→ UTC, + duration, → destination
Example18:00 Brisbane(+10) → London(0) = 08:00
Trapwatch the day change · use the offset given · ½-hour zones