# Time Zone Converter

> Converts a wall-clock date and time from one IANA time zone to another using the tz database rules built into ICU, so the daylight-saving offsets in force on that date are applied automatically. Reports both UTC offsets, the UTC instant, the weekday and the day difference.

- Calculator id: `time-zone-converter` · Category: Time & Geography (`time`) · Tool name: `convert_time_zone`
- Canonical page: https://tttkmbb.com/time/time-zone-converter · This document: https://tttkmbb.com/time/time-zone-converter.md · JSON definition: https://tttkmbb.com/time/time-zone-converter.json

## Purpose

Converts a wall-clock date and time from one IANA time zone to another using the tz database rules built into ICU, so the daylight-saving offsets in force on that date are applied automatically. Reports both UTC offsets, the UTC instant, the weekday and the day difference.

**Use when:** You need to know what time an event scheduled in one city corresponds to in another city or in UTC on a specific date.

**Do not use when:** You need the same instant in many zones at once (use world-clock), an epoch value (use unix-timestamp), or the elapsed time between two clock times (use time-duration).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `date` | date |  | optional, default "today" | Calendar date of the source time in from_zone (YYYY-MM-DD); defaults to the current UTC date. |
| `time` | string |  | required | Wall-clock time in from_zone, 24-hour HH:MM (seconds optional). |
| `from_zone` | string |  | required | IANA time zone of the source time, e.g. Australia/Adelaide, Europe/Berlin or UTC. |
| `to_zone` | string |  | required | IANA time zone to convert to, e.g. America/New_York or Asia/Tokyo. |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `converted_date` | date |  | Calendar date in to_zone. |
| `converted_time` | string |  | Wall-clock time in to_zone (HH:MM). |
| `converted_datetime` | string |  | ISO 8601 date-time in to_zone including its UTC offset. |
| `converted_weekday` | string |  | Day of the week of converted_date. |
| `from_utc_offset` | string |  | UTC offset of from_zone at that instant (±HH:MM). |
| `to_utc_offset` | string |  | UTC offset of to_zone at that instant (±HH:MM). |
| `from_abbreviation` | string |  | Short zone name from ICU (e.g. EDT); 'GMT+9:30' style when the zone has no common English abbreviation. |
| `to_abbreviation` | string |  | Short zone name of to_zone at that instant. |
| `utc_datetime` | string |  | The same instant in UTC (ISO 8601). |
| `day_difference` | integer | days | converted_date minus date: −1, 0 or +1. |
| `time_difference_hours` | number | h | to_zone offset minus from_zone offset at that instant; positive when to_zone is ahead. |

## Formula

`utc = date + time − offset_from(date, time); converted = utc + offset_to(utc); time_difference_hours = (offset_to − offset_from) / 60`

Offsets come from the IANA tz database as shipped with ICU (Intl.DateTimeFormat), including historical and future daylight-saving rules known at build time. A source time that does not exist because clocks jumped forward is moved forward by the gap; a time that occurs twice during a fall-back hour takes its first occurrence.

## Data Sources

- IANA Time Zone Database (tz) — https://www.iana.org/time-zones (standard, retrieved 2026-09-24)
- List of tz database time zones (Wikipedia) — https://en.wikipedia.org/wiki/List_of_tz_database_time_zones (reference, retrieved 2026-09-24)

Data freshness: `daily` (max_age_seconds 86400). Depends on the current date unless the date is supplied.

## API

- `GET https://tttkmbb.com/api/v1/calculate/time-zone-converter?time=…&from_zone=…&to_zone=…`
- `POST https://tttkmbb.com/api/v1/calculate/time-zone-converter` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/time-zone-converter · OpenAPI operationId `convert_time_zone` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool: `convert_time_zone` (dedicated) or `run_calculator` with `{"calculator_id": "time-zone-converter", "inputs": {…}}`

## Example

- 09:00 Adelaide → New York on 2026-09-23: inputs `{"date":"2026-09-23","time":"09:00","from_zone":"Australia/Adelaide","to_zone":"America/New_York"}` → `{"converted_date":"2026-09-22","converted_time":"19:30","converted_weekday":"Tuesday","from_utc_offset":"+09:30","to_utc_offset":"-04:00","utc_datetime":"2026-09-22T23:30:00Z","day_difference":-1,"time_difference_hours":-13.5}`
- 12:00 Los Angeles → Kolkata on 2026-07-04: inputs `{"date":"2026-07-04","time":"12:00","from_zone":"America/Los_Angeles","to_zone":"Asia/Kolkata"}` → `{"converted_date":"2026-07-05","converted_time":"00:30","from_utc_offset":"-07:00","to_utc_offset":"+05:30","utc_datetime":"2026-07-04T19:00:00Z","day_difference":1,"time_difference_hours":12.5}`

```
GET https://tttkmbb.com/api/v1/calculate/time-zone-converter?date=2026-09-23&time=09%3A00&from_zone=Australia%2FAdelaide&to_zone=America%2FNew_York
```

## Limitations

You need the same instant in many zones at once (use world-clock), an epoch value (use unix-timestamp), or the elapsed time between two clock times (use time-duration). Offsets come from the IANA tz database as shipped with ICU (Intl.DateTimeFormat), including historical and future daylight-saving rules known at build time. A source time that does not exist because clocks jumped forward is moved forward by the gap; a time that occurs twice during a fall-back hour takes its first occurrence. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Which zone names are accepted?**

IANA names such as Europe/Paris, America/Chicago, Asia/Singapore or Australia/Perth, plus UTC and fixed zones like Etc/GMT+5 (note the reversed sign). Abbreviations such as 'CST' are ambiguous and mostly not accepted.

**How is daylight saving handled?**

Automatically: the offset of each zone on the given date is looked up in the tz database, so a 9:00 Adelaide meeting in September lands at 19:30 the previous evening in New York, but at 18:30 once Adelaide starts daylight saving in October.

## Related

- [World Clock Calculator](https://tttkmbb.com/time/world-clock.md) — Show one instant in a whole list of cities.
- [Unix Timestamp Converter](https://tttkmbb.com/time/unix-timestamp.md) — Turn the same instant into Unix epoch seconds.
- [Time Duration Calculator](https://tttkmbb.com/everyday/time-duration.md) — Hours and minutes between two clock times.