Why does the offset change throughout the year?

Boston (America/New_York) observes Daylight Saving Time: clocks move forward one hour in spring and back in fall. Tokyo stays at UTC+9 year-round. The offset is 13 hours when Boston is on EDT (UTC-4) and 14 hours when Boston is on EST (UTC-5).

What time zones does this tool use?

Tokyo uses the Asia/Tokyo IANA zone (JST, UTC+9 always). Boston uses America/New_York (EST UTC-5 in winter / EDT UTC-4 in summer).

Does this handle Daylight Saving Time automatically?

Yes. The tool uses the JavaScript Intl API with named IANA zones, so DST transitions are handled by your browser automatically.

What if the converted Boston time rolls back past midnight?

The tool handles wrap-around and labels times that fall on the previous day with a "-1 day" badge so there is no ambiguity.

Is there a good overlap window for Tokyo and Boston business hours?

Overlap is very limited. Tokyo business hours (9 AM–5 PM JST) correspond to roughly 7 PM–3 AM EST (or 8 PM–4 AM EDT) in Boston, so early Tokyo morning meetings or late Boston evening calls are typically needed.

Time Difference: Tokyo to Boston

See live Tokyo and Boston clocks side by side, the exact hour offset, and convert any Tokyo hour to Boston time instantly.

Tokyo

--:--:--

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JST (UTC+9)

Current Offset

hours ahead

(Tokyo ahead of Boston)

Boston

--:--:--

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Tokyo Hour to Boston

Select Tokyo hour

Business Hours Overlap

Tokyo business hours (9 AM – 5 PM) vs Boston equivalent:

Summary

Tokyo (Asia/Tokyo, JST UTC+9) is 13 or 14 hours ahead of Boston (America/New_York) depending on US Daylight Saving Time. This tool shows both live clocks, calculates the current offset automatically, and lets you select any Tokyo hour to see the exact corresponding Boston time.

How it works

Your browser reads the current UTC time.
It converts UTC to Tokyo local time (Asia/Tokyo, UTC+9, no DST).
It converts UTC to Boston local time (America/New_York, respecting EST/EDT).
The offset is computed as the difference between the two local times.
When you pick a Tokyo hour from the selector, the tool subtracts the offset to show the Boston equivalent.

Use cases

Schedule a call between a Tokyo office and a Boston partner.
Check whether Boston colleagues are still working when you start your Tokyo morning.
Plan webinars or live streams that span both cities.
Quickly verify what time a Tokyo deadline falls in Boston.
Calculate overlap windows for remote teams split across Japan and the US East Coast.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu