Seiko Instruments · Seiko NH34 / 4R34 GMT

Seiko 5 Sports GMT and microbrand GMTs: inside the Seiko NH34 / 4R34

The Seiko 5 Sports GMT, the 5 Sports Field GMT and many microbrand GMTs run on the 4R34 or its unbranded twin, the NH34. From a full wind it runs about 41 hours, or 1.7 days.

Updated September 2026 · Based on manufacturer specs, published reviews and watchmaker/owner reports

Watches that use the Seiko NH34 / 4R34

The movement arrived in 2022 inside the Seiko 5 Sports GMT, where it's called the 4R34. Seiko Instruments sells the same design to other brands as the NH34, and it quickly became the default movement for affordable microbrand GMT watches. It's the reason a mechanical GMT with a proper fourth hand now costs about the same as a regular Seiko 5.

Whatever the name on the dial, these are all "caller" GMTs. That matters more than the brand, and it's explained below.

Specs at a glance

History and where it came from

For years, Seiko fans asked for an affordable mechanical GMT. In June 2022 Seiko answered with the 5 Sports GMT, announced with the black SSK001, blue SSK003 and orange SSK005, and in stores from July. SJX described its new 4R34 as derived from the 4R36 in the regular Seiko 5 Sports: same size, same 3 Hz beat, same 41-hour reserve, plus a 24-hour hand.

What changed the market was the unbranded version. As aBlogtoWatch noted in its Nezumi Aviera GMT review, the 4R34 was almost immediately made available to independent brands as the NH34. Before that, a small brand wanting a mechanical GMT had to pay for a Swiss ETA 2893 or a Sellita equivalent. Within a couple of years, NH34 GMTs from microbrands were everywhere. In late 2023 Seiko added the smaller 5 Sports Field GMT (SSK023 and SSK025) on the same movement.

Accuracy in the real world

Seiko rates the 4R34 at +45 to -35 seconds a day, measured on the wrist between 5°C and 35°C. SII quotes the NH34 at -20 to +40 seconds a day, but that's a static test on the bench shortly after a full wind, and its technical guide allows up to 60 seconds a day between positions. The parts are the same; the two figures just measure different things.

Real watches usually do much better than either band. aBlogtoWatch's Seiko 5 Sports GMT sample ran at about -4 seconds a day on the wrist. Owners report a wider spread than that, from a few seconds a day to a couple of dozen, which is typical for a movement that isn't finely adjusted at the factory. Like its NH35 sibling, it's easy for a watchmaker to regulate, and some microbrands regulate theirs before shipping.

Reliability and servicing

The NH34 shares almost everything with the NH35 and 4R36, which have a long record of shrugging off daily wear. The only new part of consequence is the 24-hour wheel and its setting train. There's no widely reported weakness in it so far.

Servicing works the same way as the rest of the family. A full overhaul at an independent can cost more than a new movement, so many watchmakers replace rather than rebuild. Seiko's own service centres will handle a Seiko 5 Sports GMT for a fixed price. Either way, the movement is cheap and widely available, so a tired NH34 won't end the life of the watch.

Quirks worth knowing

• It's a caller GMT, not a flyer. The 24-hour hand is the one you set on its own. On a "flyer" or traveller's GMT, you'd jump the local hour hand while travelling and leave home time on the 24-hour hand. SJX called the 4R34 "not a true GMT" for this reason. It's ideal for tracking a second zone from home, and clumsier on a trip.
• Date and GMT hand share a crown position. At the first click, turning the crown counterclockwise sets the date and clockwise moves the 24-hour hand. Time is set at the second click, which stops the seconds hand.
• Get AM and PM right. Seiko's manual warns that if the main hands are set 12 hours out, the date will change at noon. The 24-hour hand is the easiest way to check.
• Date change danger zone. Don't set the date between 9pm and 3am. Here's why.
• More to reset when it stops. A stopped NH34 means setting the time, the date and the GMT hand again. Seiko suggests about 20 turns of the crown to get it running from stopped.

How it compares

• Seiko NH35 and 4R35 / 4R36: the same movement without the 24-hour hand. The reserve, accuracy and servicing story are the same.
• ETA 2893: the Swiss caller GMT the NH34 undercut. It beats at 4 Hz and has a similar 42-hour reserve, but costs far more to buy and service.
• Miyota 9075: a true flyer GMT with a jumping local hour hand and a 42-hour reserve, used by microbrands such as Baltic and Lorier. Better for frequent travellers, at a higher price.
• Seiko 6R54: Seiko's step-up GMT in the Prospex Alpinist GMT, with a 72-hour reserve.
• Hamilton H-14: an 80-hour Swiss GMT in the Khaki Aviation Converter GMT and Khaki Navy GMT, at several times the price.

Living with the 41-hour reserve

A GMT watch makes a short reserve more annoying, because there's an extra hand to reset. Take your Seiko 5 Sports GMT off on Friday evening and it will usually stop some time on Sunday. On Monday you'll set the time at the second click, then the date and the 24-hour hand at the first, all while avoiding the evening date-change window.

It's the same with a microbrand NH34 GMT that only comes out for trips. Pack it the day before you fly and it may be close to empty by the time you land, especially if it only had a quiet desk day of charge. Watch Winder counts down the reserve for each watch you own and reminds you before it stops, so you can wear it or wind it in time. To check a particular weekend, try the "Will my watch stop?" calculator.

Verdict

The NH34 and 4R34 made the mechanical GMT affordable. You get the proven NH35 platform with hacking, hand-winding and a fourth hand, in a Seiko 5 Sports GMT or in dozens of microbrand designs. The trade-offs are the caller setting, which frequent flyers may find fiddly, and a 41-hour reserve that stops over a weekend. If you mainly track a second zone from home, it's hard to argue with.

FAQ

How long does the Seiko 5 Sports GMT run off the wrist?

About 41 hours from a full wind. Taken off on Friday evening, a Seiko 5 Sports GMT will usually stop some time on Sunday.

Is the Seiko 5 Sports GMT a true GMT?

It's a caller GMT. The 24-hour hand is set independently, while the local hour hand can't be jumped on its own, so it suits tracking a second time zone better than frequent travel.

How do you set the GMT hand on a Seiko SSK001?

Pull the crown to the first click and turn it clockwise to move the 24-hour hand; turning it counterclockwise sets the date instead. Set the main time first, at the second click.

Does the Seiko 5 Sports GMT hack and hand-wind?

Yes. The 4R34 stops the seconds hand when you pull the crown to the second click, and it can be wound by turning the crown clockwise in the normal position.

How accurate is the Seiko 5 Sports GMT?

Seiko rates the 4R34 at +45 to -35 seconds a day. Many examples run much closer, and one aBlogtoWatch review sample ran at about -4 seconds a day on the wrist.

Is the NH34 the same as the 4R34?

Yes, in construction. The 4R34 is the version Seiko uses in its own watches, and the NH34 is sold to other brands such as Nodus, Nezumi and RZE.

Is the Seiko 5 Field GMT the same movement as the SSK001?

Yes. The SSK023 and SSK025 Field GMT use the same 4R34 with the same 41-hour reserve, in a smaller 39.4 mm case.

Sources

• Seiko: Cal. 4R34 instruction manual
• Time Module (SII): Cal. NH3 series technical guide
• SJX: Seiko introduces the Seiko 5 Sports GMT
• aBlogtoWatch: Seiko 5 Sports GMT SSK005K1 review
• aBlogtoWatch: Nezumi Aviera GMT review

Watches we've reviewed with the Seiko NH34 / 4R34 GMT

• Seiko 5 Sports GMT review (SSK001, SSK003)

Keeping it running

• On an average day an automatic gains roughly 4 hours of reserve per hour on the wrist, so about 10 hours of wear fills the Seiko NH34 / 4R34 GMT. Desk days charge more slowly.
• Most automatics can also be wound by the crown. If yours has stopped, a few dozen turns gets it going before you put it on.
• Off the wrist it stops about 41 hours after it was last full. Stopped sooner?
• On a watch winder, start at about 650 turns per day, both directions. Winder settings for every movement.
• If it does stop, don't set the date between 9pm and 3am. Check if it's safe.

All Seiko movements

Never let it stop

Watch Winder counts down the reserve of every watch you own and reminds you before one stops. It already knows the Seiko NH34 / 4R34 GMT: type your watch's name and the reserve fills itself in.

Manufacturer's published figure. Real reserve varies with the watch's age and service; check your manual.