Core Data Timestamp Converter

What is a Core Data timestamp?

Apple’s Core Data framework stores Date attributes as the number of seconds since January 1, 2001 00:00:00 UTC — the same CFAbsoluteTime reference date used across macOS and iOS. When you open a Core Data store directly in SQLite, date columns (often named Z…DATE) appear as these 2001-based floating-point values.

• Epoch: 2001-01-01 00:00:00 UTC
• Type: floating-point seconds (sub-second precision preserved)
• Seen in: Core Data SQLite stores, ZDATE / Z_…_DATE columns, exported .sqlite databases
• Identical reference date to NSDate timeIntervalSinceReferenceDate

How to convert a Core Data timestamp to Unix time

Add the 978,307,200-second gap between 1970 and 2001 to rebase a Core Data value onto the Unix epoch.

• Unix seconds = CoreDataTimestamp + 978307200
• Example: 721692800 → 1700000000 → 2023-11-14 22:13:20 UTC
• SQLite: datetime(ZDATE + 978307200, "unixepoch")
• Reverse: CoreDataTimestamp = Unix seconds − 978307200

Querying Core Data SQLite stores

Reading a Core Data database directly is common in forensics and debugging. Because the values are 2001-based, a forgotten offset shifts every date ~31 years into the past. Negative values are valid and represent dates before 2001.

• Column names are usually prefixed with Z (Core Data’s internal naming)
• A value of 0 means 2001-01-01, frequently used as a default/unset date
• Times are stored in UTC; apply the display timezone afterward

What epoch does Core Data use?

Core Data stores dates as seconds since January 1, 2001 00:00:00 UTC, the same reference date as CFAbsoluteTime/NSDate.

How do I convert a Core Data ZDATE to a real date?

Add 978,307,200 to the value to get a Unix timestamp, then format it — for example, SQLite datetime(ZDATE + 978307200, "unixepoch").

Why are my Core Data dates 31 years off?

You likely treated the 2001-based value as a Unix timestamp. Add the 978,307,200-second offset to correct it.

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