When it's Tuesday afternoon in Sydney, it's still Monday in New York. UTC is the anchor — know a city's offset, and you can always find the time anywhere on Earth.
Use the PDF for classwork, homework or revision. It includes key ideas, activities, questions, an extend task and success-criteria proof.
You book a video call with a friend in London for "9 am their time" on a Tuesday in January. Sydney is in summer, London is in winter — no daylight saving in the UK. When should you set your alarm in Sydney? What information do you need, and how do you use it?
Type your initial response below — you will revisit this at the end of the lesson.
Write your initial response in your book. You will revisit it at the end of the lesson.
Come back to this at the end of the lesson.
Wrong: Sydney is always 10 hours ahead of London.
Right: Sydney is 10 hours ahead of London in winter, but 11 hours ahead during Australian daylight saving time (AEDT). The difference changes with the seasons.
Key Time Zones Reference
Always check your units before substituting into formulas. Converting to consistent units is a common source of errors in assessment tasks.
| City / Region | Standard offset | Daylight saving offset |
|---|---|---|
| UTC / London (GMT, winter) | UTC+0 | UTC+1 (BST, summer) |
| New York (EST) | UTC−5 | UTC−4 (EDT) |
| Los Angeles (PST) | UTC−8 | UTC−7 (PDT) |
| Dubai | UTC+4 | None |
| India (IST) | UTC+5:30 | None |
| Singapore / Perth (AWST) | UTC+8 | None |
| Tokyo / Seoul | UTC+9 | None |
| Darwin / Adelaide (ACST) | UTC+9:30 | UTC+10:30 (ACDT) — SA only |
| Sydney / Melbourne / Brisbane (AEST) | UTC+10 | UTC+11 (AEDT) — NSW, VIC, TAS, ACT only |
| Auckland (NZST) | UTC+12 | UTC+13 (NZDT) |
It is 1400 UTC on a Wednesday. What is the local time in:
It is 3:30 pm Thursday in Sydney during daylight saving (AEDT = UTC+11). What is the time in:
In January (Australian summer), it is 9:00 am in Brisbane. What is the time in Sydney at that moment? (Brisbane observes AEST all year; Sydney observes AEDT in January.)
Section A — UTC Conversions
Section B — City to City
Section C — Daylight Saving
(a) $0600+10=\mathbf{1600}$ (b) $0600+8=\mathbf{1400}$ (c) $0600-5=\mathbf{0100}$
$1800 - 10 = \mathbf{0800 \text{ UTC}}$
$2230 - 8 = \mathbf{1430 \text{ UTC}}$
Sydney 1400 AEST; UTC = 1400−10 = 0400; (a) Adelaide ACST = 0400+9.5 = $\mathbf{1330}$ (1:30 pm); (b) Tokyo = 0400+9 = $\mathbf{1300}$ (1:00 pm); (c) London = 0400+0 = $\mathbf{0400}$ (4:00 am)
Dubai 1030 UTC+4 → UTC = 1030−4 = 0630; LA = 0630−8 = −0130 → add 2400 → $\mathbf{2230}$ previous day (10:30 pm)
Auckland 1500 UTC+12 → UTC = 1500−12 = 0300; Sydney AEST = 0300+10 = $\mathbf{1300}$ (1:00 pm)
Sydney AEDT (UTC+11) 1000; UTC = 1000−11 = 2300 (prev day)... or directly: Brisbane AEST is 1 hour behind AEDT; Brisbane time = $\mathbf{0900}$ (9:00 am)
Adelaide ACDT = UTC+10:30; UTC = 0800 − 10h30 = 2130 prev day... 0800 − 10 = 2200−0:30 = $\mathbf{2130 \text{ UTC}}$ previous day
Look back at what you wrote in the Think First section. What has changed? What did you get right? What surprised you?
Multiple Choice
1 It is 0300 UTC. What is the time in Sydney using AEST (UTC+10)?
? 1 It is 0300 UTC. Identify the time in Sydney using AEST (UTC+10)?
2 In July (Australian winter), Sydney is on AEST (UTC+10) and London is on BST (UTC+1). The time difference between Sydney and London in July is:
? Regarding this topic, 2 In July (Australian winter), Sydney is on AEST (UTC+10) and London is on BST (UTC+1). The time difference between Sydney and London in July is:
3 It is 11:00 pm Wednesday in Perth (AWST = UTC+8). What is the time and day in Auckland (NZST = UTC+12)?
? 3 It is 11:00 pm Wednesday in Perth (AWST = UTC+8). Identify the time and day in Auckland (NZST = UTC+12)?
Short Answer
SA 4 3 marks A live international sports event is broadcast from Tokyo at 8:00 pm local time (JST = UTC+9) on a Saturday.
(a) Convert the Tokyo broadcast time to UTC. (1 mark)
(b) What time should a Sydney viewer (AEST = UTC+10) tune in? (1 mark)
(c) What time should a New York viewer (EST = UTC−5) tune in, and is it the same day? (1 mark)
$2000 - 9 = \mathbf{1100 \text{ UTC Saturday}}$
$1100 + 10 = \mathbf{2100 \text{ Saturday}}$ (9:00 pm Sydney)
$1100 - 5 = \mathbf{0600 \text{ Saturday}}$ (6:00 am); same Saturday but 14 hours earlier than Tokyo
SA 5 4 marks In January, a business call is scheduled between a Sydney office (AEDT = UTC+11) and a London office (GMT = UTC+0). Both parties agree to meet at 9:00 am London time.
(a) What time is 9:00 am London time in UTC? (1 mark)
(b) What time must the Sydney office join the call? (1 mark)
(c) Is Sydney on the same day as London for this call? (1 mark)
(d) If the call moves to July (London still UTC+0, Sydney now AEST = UTC+10), what time must Sydney now join? (1 mark)
London = UTC+0; so 9:00 am London = 0900 UTC
$0900 + 11 = \mathbf{2000}$ (8:00 pm AEDT)
Yes — 8:00 pm Sydney is the same calendar day as 9:00 am London
July: Sydney AEST = UTC+10; $0900 + 10 = \mathbf{1900}$ (7:00 pm AEST) — 1 hour earlier than in January
SA 6 4 marks A flight departs Sydney at 11:30 pm AEDT (UTC+11) on a Sunday and arrives in Dubai 14 hours 20 minutes later. Dubai uses UTC+4 all year.
(a) Convert Sydney departure time to UTC. (1 mark)
(b) Find the UTC arrival time. (1 mark)
(c) Find the local Dubai arrival time. (1 mark)
(d) Is it still Monday in Dubai when the plane lands, or has it become Tuesday? (1 mark)
$2330 - 11 = \mathbf{1230 \text{ UTC Sunday}}$
$1230 + 14\text{h}20 = \mathbf{0250 \text{ UTC Monday}}$ (crosses midnight: $1230+14=0230$ Monday, $+20\text{min}=0250$)
$0250 + 4 = \mathbf{0650 \text{ Dubai local}}$ (6:50 am)
UTC arrival is Monday 0250; Dubai local = 0650 → still Monday in Dubai
Time Zones and UTC