Timezone & Date Math Calculator
Enter a date/time and convert it between a source and target timezone (DST handled via the browser's IANA database), with an optional date-math offset like +2d 3h, -90m, 1w, or ISO-8601 PT30M. The output shows UTC, both zones, ISO, and epoch, and warns about nearby DST changes. The World clock and Business days tabs add a multi-city table and weekday math. Runs in your browser.
Auto-converts as you type. Ctrl+Enter to re-run.
How to use the Timezone & Date Math Calculator
One calculator for the date and time problems engineers hit every week: convert timestamps across time zones, plan release / incident / on-call windows, do calendar or fixed-duration date math, compute SLA deadlines that respect business hours and holidays, parse ISO 8601 durations like P3DT4H30M, and produce ready-to-paste timezone tables for Slack or Teams. Runs locally in your browser using the IANA timezone database that ships with modern browsers.
What it does
- Single timezone conversion: same instant in source and target zones with DST handled.
- Multi-zone table: same moment across many zones for release / meeting announcements.
- Date math: add or subtract years, months, weeks, days, hours, minutes, seconds.
- Business-day math: skip weekends and a holiday list; respect business hours.
- SLA deadline: from start + duration with weekend rule, business hours, holidays.
- ISO 8601 duration parser and emitter (
P3DT4H30M,PT15M). - Date range inspector: difference, total days, calendar weeks, working days.
- Export an .ics file or generate a Google Calendar link from any computed time.
When to use it
- Translate a support incident timestamp between regional teams.
- Schedule a release across UTC / PST / IST / EST and produce a paste-ready table.
- Add 5 business days to an SLA start time, skipping holidays.
- Parse an ISO duration that came back from an API (
retry_after=PT2M). - Decide whether a token issued at one time is still valid right now in your zone.
- Compute the elapsed time across DST boundaries correctly.
How to use it
- Convert: enter source date/time and source/target zones. The same instant is shown in both.
- Multi-Zone: pin several zones for a single moment.
- Date math: pick the unit and offset; toggle calendar vs fixed-duration semantics.
- Business / SLA: set weekend rule, business hours, holiday list, then compute the deadline.
- Duration: paste an ISO 8601 string or human-friendly duration to break it down.
- Date range: enter start and end and read the difference in multiple units.
- Calendar: download
.icsor open Google Calendar from the computed time.
Tips & pitfalls
- Always include a timezone offset (
+05:30) or trailingZwhen the source timestamp is absolute. - Adding 24 hours is not always one calendar day across DST — use calendar mode to keep wall-clock time.
- Adding 1 month at month-end (e.g. Jan 31) clamps to the last day of the next month.
- Holidays you enter are stored locally — verify against your business calendar before publishing an SLA result.
- "Local" time depends on the device — always specify the zone explicitly for production calculations.
- Use IANA names (
America/Los_Angeles), not abbreviations like PST that change with DST.
FAQ
- How do I convert a time between zones? Enter the source date/time and zone, pick the target zone — the same instant is shown in the new wall clock.
- How do I add business days? Use the Date math or Business / SLA tab — weekends and the holiday list you provide are skipped automatically.
- What is an ISO 8601 duration? A format like
P3DT4H30Mmeaning 3 days, 4 hours, 30 minutes. Common in APIs. - Does it handle DST? Yes — using the IANA database in the browser. Conversions span DST boundaries correctly.
- Is anything uploaded? No. All math runs in your browser.
- How do I share a release window across teams? Use Multi-Zone and copy the table directly into Slack, Teams, or email.
Runs locally in your browser using the IANA timezone database. No uploads. Holidays you configure stay in your browser.