Methodology
Current time and UTC offsets
Every live clock on this site is computed using the JavaScript Intl.DateTimeFormat API against a specific IANA time zone identifier (for example America/New_York or America/Kentucky/Louisville). The IANA database is maintained as a public, open-source project and is built directly into every modern browser and server runtime, so it reflects the correct offset and daylight saving status for any date without us maintaining a separate offset table.
State and city time zone assignments
Each state, territory, and city on this site is assigned the specific IANA zone identifier that correctly reflects its real-world daylight saving observance — including the fourteen states with territory in more than one zone, and county- or region-specific identifiers (such as Indiana's or North Dakota's separate zone entries) where the standard tzdata database provides one.
Daylight saving transition dates
Daylight saving start and end dates are calculated using the current US federal rule: the second Sunday in March and the first Sunday in November, in effect since 2007 under the Energy Policy Act of 2005. States and territories that don't observe daylight saving are excluded from these calculations.
Sunrise and sunset
Sunrise and sunset times are calculated from each location's latitude and longitude using standard solar position equations, accurate to within a minute or two — the same class of calculation used by most public astronomical calculators.
Population figures
City and state population figures are approximate, order-of-magnitude estimates used for ranking and display purposes, not official census figures.