Date & Time Toolkit
Date difference, add/subtract, day information, and multi-format date formatting.
Date and time converter toolkit: differences, arithmetic, formatting, and Unix timestamps in one place
Working with dates in software is notoriously tricky: APIs return Unix timestamps, databases store ISO 8601 strings, users expect human-readable formats, and business logic demands date arithmetic. Switching between tools wastes time. AlteredIdea's date and time toolkit consolidates everything into four focused tabs: all running locally in your browser.
The Date Difference tab handles the common need to know exactly how many years, months, and days separate two dates: useful for age calculation, contract durations, and deadline tracking. The Add/Subtract tab lets you compute a future or past date by adding or subtracting days, weeks, months, or years. The Formatter tab converts a single date into eight standard formats simultaneously, with one-click copy for each. Every result updates in real time as you type.
How to convert: step by step
- 1Choose a tab
Select Date Difference, Add/Subtract, Day Info, or Formatter depending on what you need to do. - 2Enter your date(s)
Use the date pickers to select dates. They default to today so you can start calculating immediately. - 3Read the result
Results update instantly: no need to click a convert button. Differences show years, months, days, total days, and weeks. - 4Switch to the Formatter tab for multiple formats
Enter a single date and see it rendered as ISO 8601, US, EU, Long, Short, Unix timestamp, RFC 2822, and more simultaneously. - 5Copy any value
Each formatted output in the Formatter tab has an inline copy button so you can grab the exact format you need.
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Frequently Asked Questions
- How do I convert a date to a Unix timestamp?
- Go to the Formatter tab, enter your date, and read the Unix Timestamp row. The value is the number of seconds since 1 January 1970 00:00:00 UTC.
- What is ISO 8601 date format?
- ISO 8601 is an international standard for representing dates and times. The full format looks like 2025-01-15T14:30:00.000Z. It is unambiguous, sortable lexicographically, and widely accepted by APIs and databases.
- How is the date difference calculated?
- The difference is broken into complete years, remaining months, and remaining days: similar to how you would count age. Total days and total weeks are also shown for convenience.
- Can I calculate a date 90 days from today?
- Yes. Go to the Add/Subtract tab, set the base date to today, enter 90, and choose Days as the unit. The result date is displayed instantly.
- What is an ISO week number?
- ISO 8601 defines weeks as starting on Monday. Week 1 is the week containing the first Thursday of the year. The Day Info tab shows the ISO week number for any date you enter.
- Does the tool handle leap years?
- Yes. The Day Info tab explicitly shows whether a year is a leap year, and date arithmetic accounts for February 29 correctly.
- What is RFC 2822 date format?
- RFC 2822 is the format used in email headers, for example: Wed, 15 Jan 2025 14:30:00 +0000. It includes the day name, day number, month abbreviation, year, time, and timezone offset.
- Is the converter affected by my local timezone?
- The Formatter tab uses your local timezone for formats that include time. The Unix Timestamp and ISO 8601 outputs are always in UTC. Date difference and add/subtract operate on calendar dates only, so timezone does not affect them.
- Can I calculate how many business days are between two dates?
- The current tool calculates calendar days and weeks. Business-day calculation is not yet supported, but total days and weeks are shown so you can estimate manually.
AlteredIdea vs alternatives
vs online converters that send data to servers: AlteredIdea converts entirely in your browser. Sensitive data never leaves your device.
vs writing conversion scripts: Instant results with no coding. Paste, convert, copy.
vs paid tools: Completely free, no account, no file size limits.