Enter one date format and convert it instantly
Use the responsive grid below. Large screens show three columns, medium screens show two, and mobile screens show one.
Sample conversion scenarios
| Source Format | Input | Equivalent UTC Date-Time | Unix Seconds | ISO Week Date |
|---|---|---|---|---|
| Gregorian / ISO | 2026-03-09 14:30:00 | 2026-03-09 14:30:00 UTC | 1773066600 | 2026-W11-1 |
| Unix Timestamp | 1773066600 | 2026-03-09 14:30:00 UTC | 1773066600 | 2026-W11-1 |
| Ordinal Date | 2026-068 | 2026-03-09 00:00:00 UTC | 1773014400 | 2026-W11-1 |
| ISO Week Date | 2026-W10-1 | 2026-03-02 00:00:00 UTC | 1772409600 | 2026-W10-1 |
Core conversion formulas
Unix timestamp
Unix seconds measure elapsed seconds from 1970-01-01 00:00:00 UTC. Milliseconds are seconds multiplied by 1,000.
Julian Date
Julian Date = (Unix seconds ÷ 86,400) + 2,440,587.5. Modified Julian Date = Julian Date − 2,400,000.5.
ISO week date
ISO week output uses year-week-weekday notation. Week 01 is the first week containing Thursday in that ISO year.
Ordinal date
Ordinal date stores a year plus day number. Day of year = calendar day index starting from 001.
Excel serial date
Excel serial values count days from a base date. The 1900 system includes the historical leap-year bug.
Timezone handling
The converter normalizes the source moment, moves it to UTC, then renders the final output in your chosen timezone.
Steps for accurate conversions
- Choose the source format that matches your original value.
- Enter the source value using the shown example pattern.
- Select the input timezone used by the original date or timestamp.
- Pick the output timezone you want for display.
- If you are converting an Excel serial, choose the 1900 or 1904 system.
- Set your preferred decimal places for numeric fields.
- Press Convert Date to show the result above the form.
- Use the CSV or PDF buttons to save the result for logs, QA notes, import mapping, or documentation.
Common questions
1. What date standards can this calculator convert?
It converts Gregorian or ISO date-time strings, Unix timestamps, Julian Date, Modified Julian Date, Excel serial dates, ISO week dates, and ordinal dates.
2. Does the tool support Unix milliseconds?
Yes. Large Unix values are automatically treated as milliseconds. The result table also shows both seconds and milliseconds for easy verification.
3. Why do Excel dates sometimes look one day off?
Excel’s 1900 date system contains a known leap-year bug. This calculator handles that behavior and warns about serial 60, which maps to a non-existent date.
4. What is the difference between Julian Date and Modified Julian Date?
Modified Julian Date is just Julian Date minus 2,400,000.5. It keeps values shorter and is common in scientific and software workflows.
5. How does timezone selection affect the output?
The converter first resolves the source moment, normalizes it to UTC, and then shows final outputs using your selected output timezone.
6. Can I use this for API payload checks and data migrations?
Yes. It is useful for validating imported dates, log timestamps, spreadsheet serials, and cross-system time fields during migration or QA work.
7. Why does ISO week year differ from the calendar year sometimes?
ISO weeks follow their own year boundary. Early January or late December dates can belong to the previous or next ISO week year.
8. What export options are included?
After conversion, you can download the result table as CSV or PDF. Both options are useful for sharing and recordkeeping.