01
Choose an ICS file
Open a calendar file that uses Windows-style timezone labels or standard IANA labels.
Business Tools
ICS Timezone Normalizer
Normalize known Windows timezone labels in an ICS file without shifting event times or deleting recurrence rules.
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Data handling
Storage and export controls
- Retention
- The tool's working state is kept only while this page is open. Inputs and results are not saved to persistent storage by Got A Tool.
- Export
- The tool may prepare a result after you run it. It downloads or copies it only when you choose that action.
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How it works
Normalize known timezone labels without moving event clocks
02
Review the changes
Known Windows labels are mapped to verified IANA names; unknown labels stay unchanged for review.
03
Download a new ICS file
Save the normalized calendar copy while keeping event times and supported calendar fields intact.
When to use it
Repair a known Windows timezone label before sharing a calendar
Calendar exports from Outlook and other applications can use Windows timezone names where another calendar expects IANA names. This tool updates only labels in its verified map, including matching VTIMEZONE and event references. It does not reinterpret a local clock as UTC, so a 09:00 event remains 09:00 after a supported label is normalized.
Questions
ICS Timezone Normalizer details
Which timezone labels can be changed?
Only known Windows-to-IANA mappings included in this version are changed. An unknown TZID is kept unchanged and shown as a review item.
Will it shift event times?
No. The tool changes a supported timezone label without changing the local DTSTART or DTEND clock value.
Are recurring events and alarms removed?
No. The normalizer preserves recurrence rules, exceptions, attendees, alarms, descriptions, and other calendar fields it does not need to change.
What happens to a non-UTC UNTIL value?
It is kept unchanged and shown for review because adding a UTC suffix would change its meaning.
Is my calendar uploaded?
No. The ICS file is read, reviewed, and written locally in your browser.
Practical guide
Read the Calendar import checklist
Review timezones, recurring events, and the receiving calendar's preview before you import or share a working copy.
Open the guide →Keep working
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