The quick answer: two windows, one rule
Pick up the phone at 18:00 Sydney time on a July day in 2026 and London picks up at 09:00. That is the start of the business day. Useful.
Dial the same London number at 09:00 Sydney time on that same July morning and you get London at 00:00. Midnight. Not useful.
Sydney is always ahead of London. The gap ranges from 9 hours in the northern summer to 11 hours in the northern winter. The best calling windows shift by two hours between seasons, and the reason is entirely down to daylight saving.
How the gap changes: January vs July
On 15 January 2026, London is on GMT (UTC+0). Sydney is on AEDT (UTC+11). The difference is 11 hours. Sydney is 11 hours ahead.
- 09:00 Sydney = 22:00 London (previous evening)
- 12:00 Sydney = 01:00 London
- 17:00 Sydney = 06:00 London
- 18:00 Sydney = 07:00 London
- 20:00 Sydney = 09:00 London
On 15 July 2026, London has switched to BST (UTC+1). Sydney is on AEST (UTC+10). The gap narrows to 9 hours.
- 09:00 Sydney = 00:00 London
- 12:00 Sydney = 03:00 London
- 17:00 Sydney = 08:00 London
- 18:00 Sydney = 09:00 London
- 20:00 Sydney = 11:00 London
London gains an hour of daylight in its summer. Sydney loses an hour of daylight saving in its winter. The two shifts partially cancel each other out.
The two best windows
In Sydney’s summer (October to March)
London is on GMT. The gap is 11 hours. Call between 18:00 and 20:00 Sydney time. That lands between 07:00 and 09:00 in London. You catch the early morning, before the London workday gets busy.
In Sydney’s winter (April to September)
London is on BST. The gap is 9 hours. Call between 17:00 and 19:00 Sydney time. That lands between 08:00 and 10:00 in London. You catch the start of the core office hours.
Why you should aim for London mornings, not afternoons
London office hours run roughly 09:00 to 17:00 local time. The London Stock Exchange opens at 08:00. Most shops open at 09:00. Lunch is typically 12:00 to 14:00. After 17:00, people leave.
Sydney’s late afternoon and early evening (17:00 to 20:00) aligns with London’s morning (07:00 to 10:00). That is the only reliable overlap. Call Sydney morning (09:00 to 12:00) and you reach London overnight or very early. Call Sydney midday and you reach London in the middle of the night.
There is no good window for Sydney to call London’s afternoon. London’s 14:00 is Sydney’s 01:00 (summer) or 23:00 (winter). Sleep time.
The worked example
You need to speak to someone in London on Tuesday 21 July 2026. London is on BST, gap is 9 hours.
You want to call at 09:30 London time, just after the market opens. 09:30 London + 9 hours = 18:30 Sydney time.
Set your alarm for 18:25 Sydney time. After work, before dinner. The person in London has just sat down at their desk. Good.
Now you need to speak to someone on Tuesday 19 January 2027. London is on GMT, gap is 11 hours.
You want to call at 08:00 London time. 08:00 London + 11 hours = 19:00 Sydney time.
Call at 19:00 Sydney time. The person in London is starting their day. You are in your evening. It works.
What to avoid
- Calling Sydney morning to London. 09:00 Sydney = 22:00 London (summer) or 20:00 London (winter). Both are outside office hours.
- Calling Sydney lunchtime. 12:00 Sydney = 03:00 London (summer) or 01:00 London (winter). You wake someone up.
- Calling on UK public holidays. London’s office workers take the day off on New Year’s Day, Good Friday (Friday 3 April 2026), May Day (Monday 4 May 2026), Spring Bank Holiday (Monday 25 May 2026), Christmas Day, and Boxing Day. A call on those days will go to voicemail.
The mental model
Sydney runs late. London runs early. The sun rises in London at 04:42 on the longest day (21 June 2026) and sets at 15:53 on the shortest (21 December 2026). When London has long days, the gap to Sydney is smaller. When London has short days, the gap is larger.
You do not need to memorise the exact date of every clock change. You only need to know two things:
- From late March to late October, London is on BST. Gap is 9 hours. Call Sydney 17:00-19:00.
- From late October to late March, London is on GMT. Gap is 11 hours. Call Sydney 18:00-20:00.
The clocks go forward on Sunday 29 March 2026 at 01:00 London time. They go back on Sunday 25 October 2026 at 02:00 London time. Mark those dates. They switch your window.
What to do next
If you are scheduling a regular call, do not guess. Use a meeting planner that respects time zones, or check the current time in London on the London time zone page. For a deeper breakdown of how the gap behaves across the year, see the London vs Sydney time guide.
The simplest practical rule: call Sydney evening, London morning. Never the reverse.