Seiko · Seiko 4R35 / 4R36

Seiko 5 Sports, Turtle and Cocktail Time power reserve: inside the 4R35 / 4R36

The Seiko 5 Sports, Prospex Turtle, Samurai, Monster and Presage Cocktail Time all run on Seiko's 4R35 or 4R36. From a full wind they run 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 4R35 / 4R36

If you own an affordable automatic Seiko made in the last decade, it very likely has a 4R35 or 4R36 inside. The 4R36 shows the day and date and powers the Seiko 5 Sports, the Turtle and the Monster. The date-only 4R35 is in the Samurai and most time-and-date Presage models. Outside Seiko, the same design is sold as the NH35 and NH36.

Specs at a glance

History and where it came from

The 4R family arrived around 2011 to replace the 7S26 in Seiko's entry-level automatics. In Seiko's own words, the 4R35 was developed from the 7S and 6R designs with two additions: manual winding and a stop-seconds function. Those were exactly the two things owners of the SKX007 and SNK809 had been asking for.

There have been two versions of the 4R35. The 4R35B replaced the original 4R35A with new parts that don't interchange, although the complete movements are the same size. Caliber Corner found that Seiko's tech sheet listed the 4R35B at 24 jewels, but real movements are marked 23 jewels, and Seiko confirmed 23 when asked. Seiko's current manual agrees: 23 jewels for the 4R35 and 24 for the 4R36.

Today the 4R36 is the heart of the Seiko 5 Sports range, which relaunched in 2019 with the SKX-style SRPD models, and of the Turtle and Monster divers. The 4R35 is the quieter-looking sibling in the Samurai, Cocktail Time and Style60's.

Accuracy in the real world

Seiko rates the 4R35 and 4R36 at +45 to -35 seconds a day, measured on the wrist between 5°C and 35°C with the watch fully wound. Seiko's manual adds the usual caveat: the real rate depends on how long you wear it, temperature, arm movement and how fully wound it is.

Real results are usually much tighter than the spec. Owners commonly report 5 to 20 seconds a day fast, with some examples running near zero and a few drifting toward the edge of the band. Long-time owners on watch forums describe 4R36s running within a handful of seconds a day with daily wear, while others see 10 to 20. Because it isn't adjusted in multiple positions at the factory, the rate varies with position and wind state, so a Seiko 5 left crown-down overnight can behave differently from one worn all day.

A watchmaker can regulate it closer to zero cheaply, and many hobbyists do it themselves.

Reliability and servicing

The 4R has the same reputation as the NH35: robust, forgiving and easy to fix. It uses Seiko's Diashock protection and Magic Lever winding, a simple bidirectional system that has been proven over decades.

When it needs attention, many independent watchmakers find a movement swap cheaper than a full overhaul, because a new NH35 or NH36 costs less than a strip-down service. Seiko's own service centres will service it too, usually for a fixed price that can approach the cost of a new Seiko 5. Either way, the movement shouldn't be what ends the watch's life.

Quirks worth knowing

• Rotor spin. The rotor freewheels in one direction, so you'll hear or feel a whirr on brisk movement. It's normal.
• Setting the day on a 4R36. At the first crown position, counterclockwise sets the date and clockwise sets the day. Some models have a bilingual day wheel, so you choose the language as you go.
• Different danger zones. Seiko's manual says don't set the date on a 4R35 between 9pm and 1am. On a 4R36, avoid 9pm to 4am, because the day changes at around 4am. Here's why.
• AM and PM. If you set the time 12 hours out, the date will flip at noon instead of midnight. Advance the hands until the date changes, and you know you're in the morning.
• Winding from stopped. Seiko suggests about 20 turns of the crown to get a stopped watch going. That starts it, but doesn't fill it.
• Magnetism. A sudden jump to minutes fast a day usually means it's magnetised. Demagnetising is quick.

How it compares

• NH35 / NH36: effectively the same movement for other brands. SII quotes -20 to +40 s/day, but that's a bench test, not the on-wrist figure Seiko uses for the 4R.
• Seiko 7S26: the SKX007 and SNK809 movement. Just as tough, but it can't be hand-wound or hacked.
• Seiko 4R37 and 4R34: the same platform with extras. The 4R37 adds a 24-hour AM/PM hand. The 4R34 (NH34 outside Seiko) adds an independently set GMT hand.
• Seiko 6R35: Seiko's step up, in the Alpinist, Sumo and pricier Presage. It has a 70-hour reserve and a tighter +25/-15 spec.
• Miyota 8215 and Orient F6922: the nearest rivals at the price. The Miyota doesn't hack. The Orient in the Kamasu and Mako hacks and hand-winds, with a similar 40-hour reserve.

Living with the 41-hour reserve

Take your Seiko 5 Sports off on Friday evening and it will usually have stopped by sometime on Sunday. A Turtle or Samurai that only comes out at weekends will be dead by the following Saturday. The 4R also charges slowly on quiet desk days, so it may not start the evening full.

A stopped 4R36 takes a little care to reset: set the time, then the day and date, and stay out of the 9pm-to-4am window. If one of these Seikos shares your wrist with others, it'll usually be the first to stop. Watch Winder counts down the reserve for each watch you own and reminds you before it stops. For a one-off check, try the "Will my watch stop?" calculator.

Verdict

The 4R35 and 4R36 aren't exciting movements, but they're the right ones for the watches they power. They're dependable, cheap to keep running, and they hack and hand-wind. Most examples keep time far better than the loose spec suggests. The short reserve is the one thing you'll notice day to day, especially if your Seiko 5, Turtle or Cocktail Time is one of several watches you rotate.

FAQ

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

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

Does the Seiko 5 Sports hack and hand-wind?

Yes. The current Seiko 5 Sports uses the 4R36, which stops the seconds hand when you pull the crown to the second click and can be wound by turning the crown clockwise.

How accurate is the Seiko Turtle?

The Turtle's 4R36 is rated at +45 to -35 seconds a day on the wrist. Most owners report a gain of roughly 5 to 20 seconds a day.

What movement is in the Seiko Presage Cocktail Time?

The standard Cocktail Time uses the 4R35, a 23-jewel automatic with hacking, hand-winding, a date and about 41 hours of power reserve.

Why did my Seiko Samurai stop overnight?

Usually because it wasn't fully wound. The 4R35 holds about 41 hours when full, but a few hours of desk wear adds much less, so wind it by the crown or wear it longer before taking it off.

Is the 4R36 the same as the NH36?

Essentially yes. The 4R36 is the version Seiko uses in its own watches, and the NH36 is sold to other brands. Seiko quotes an on-wrist accuracy band for the 4R, while SII quotes a bench figure for the NH.

What's the difference between the 4R35 and the 4R36?

The 4R36 adds a day-of-week display and has 24 jewels to the 4R35's 23. Power reserve, accuracy and size are otherwise the same.

Sources

• Seiko: Cal. 4R35/4R36/4R37 instruction manual
• Caliber Corner: Seiko Caliber 4R35
• Seiko: 5 Sports SRPD55 specifications
• Professional Watches: Seiko Prospex SRPD25 and SRPD27 Monster review

Watches we've reviewed with the Seiko 4R35 / 4R36

• Seiko 5 Sports review (SRPD)
• Seiko Presage Cocktail Time review
• Seiko Presage Style60's review
• Seiko Prospex Samurai review (43.8mm and King Samurai)
• Seiko Prospex Turtle review (SRPE93 and King Turtle)

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 4R35 / 4R36. 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 4R35 / 4R36: 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.