Swift Date Format Converter

Q: What does ISO8601DateFormatter output?

By default: **`2026-08-13T14:30:00Z`**. With `.withInternetDateTime` options you get `2026-08-13T14:30:00+00:00`.

Q: What is the difference between ISO8601DateFormatter and DateFormatter?

`ISO8601DateFormatter` is a **strict ISO 8601** formatter with fixed options; `DateFormatter` is a flexible, locale-aware formatter using Unicode patterns. Prefer ISO8601DateFormatter for interchange.

Swift's `ISO8601DateFormatter` emits strict ISO 8601 strings (`2026-08-13T14:30:00Z`), while `DateFormatter` uses Unicode locale patterns (`yyyy-MM-dd HH:mm:ss`). Getting them wrong is a classic `DateFormatter` "returns nil" bug on iOS.

This converter renders your date-time in the `ISO8601DateFormatter` default form and the equivalent `DateFormatter` pattern so you can debug date parsing in Swift apps.

Timezone:

Enter a date-time above to see the conversion results.

Swift Date Format Converter Quick Reference

Format	Pattern / Description	Example 1	Example 2
Swift / Cocoa String	yyyy-MM-dd HH:mm:ss Z	2026-08-13 14:30:00 +0000	2026-01-01 00:00:00 +0000

* Examples are rendered in UTC for the fixed sample instants above.

When to Use Swift Date Format

API parsing on iOS

Verify the timestamp shape your backend returns matches `ISO8601DateFormatter` defaults before writing parsing code.

DateFormatter nil debugging

When `DateFormatter.date(from:)` returns nil, compare the input string against the formatter pattern to find the mismatch.

Codable date strategy

Choose the right `JSONDecoder.DateDecodingStrategy` (`.iso8601`, `.formatted`) by matching your API's actual timestamp format.

Frequently Asked Questions

What does ISO8601DateFormatter output?

By default: `2026-08-13T14:30:00Z`. With `.withInternetDateTime` options you get `2026-08-13T14:30:00+00:00`.

Why does my DateFormatter return nil?

The input string does not exactly match the pattern. Common mismatches: missing `Z` for UTC, wrong locale (`en_US_POSIX` needed), or fractional seconds not in the pattern.

What is the difference between ISO8601DateFormatter and DateFormatter?

`ISO8601DateFormatter` is a strict ISO 8601 formatter with fixed options; `DateFormatter` is a flexible, locale-aware formatter using Unicode patterns. Prefer ISO8601DateFormatter for interchange.

What DateFormatter pattern matches ISO 8601?

`yyyy-MM-dd'T'HH:mm:ssXXXXX` with `locale = en_US_POSIX` and `timeZone = UTC` — the standard workaround for pre-iOS 10 parsing.

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All Format Guides

Unix Timestamp ISO 8601 ISO Week Date ISO Ordinal Date Military Time Decimal Time RFC 2822 RFC 3339 SQL Datetime Julian Date HTTP Date Excel Serial Date GPS Time UTC Time Cron Expression

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