New Zealand has two time zones. The main islands use New Zealand Standard Time (NZST), 12 hours in advance of Coordinated Universal Time (UTC) / military M (Mike), while the outlying Chatham Islands use Chatham Standard Time (CHAST), 12 hours 45 minutes in advance of UTC / military M^ (Mike-Three). During summer (last Sunday in September until the first Sunday in April) daylight saving time is observed and clocks are advanced one hour. New Zealand Daylight Time (NZDT) is 13 hours ahead of UTC, and Chatham Daylight Time (CHADT) 13 hours 45 minutes ahead.