NH35 vs NH36: Comparing Seiko Automatic Movements for Mods

If you're planning a Seiko mod, sooner or later you'll run into this question: NH35 or NH36? Both movements come from the same family, both are robust, both are serviceable worldwide. But they have one decisive difference — and it determines which dial you can actually install.

The short answer

NH35: Automatic with date (single display at 3 o'clock) NH36: Automatic with date AND day of the week (dual display at 3 o'clock)

If you want to build a day-date dial in the style of a Rolex Day-Date or a classic Seiko 5 Sports, you need the NH36. For every other dial layout, the NH35 is the right choice.

Technical specs compared

Spec	NH35	NH36
Manufacturer	Seiko Instruments Inc. (SII)	Seiko Instruments Inc. (SII)
Beat rate	21,600 bph (6 Hz)	21,600 bph (6 Hz)
Power reserve	41 hours	41 hours
Jewels	24	24
Hand-winding	Yes	Yes
Hacking function	Yes	Yes
Date	Yes	Yes
Day of week	No	Yes (bilingual: usually EN/Kanji or EN/SP)
Movement diameter	27.4 mm	27.4 mm
Movement height	5.32 mm	5.32 mm
Factory accuracy	-20 to +40 s/day	-20 to +40 s/day
After regulation	±10 s/day realistic	±10 s/day realistic

Functionally, the two movements are identical. Both run at 21,600 bph (that gives the seconds hand 6 ticks per second — a bit less fluid than high-beat movements at 28,800 bph, but more power-efficient in return). Both accept a screw-down crown and run reliably in any standard position.

Where the difference actually matters

Dial compatibility. This is the crux of it. A dial designed for the NH35 (single date window at 3 o'clock) will not fit an NH36 — the day window either stays empty or ends up in the wrong spot. And the reverse is just as true: an NH36 day-date dial won't fit an NH35.

Hand shaft. Both movements share identical hand-shaft dimensions, so you can use the same hand sets on either one.

Date-setting. The crown has three positions on both movements: 1) winding, 2) date/day setting, 3) time setting with hacking. On the NH36, in position 2 you set the date by turning one direction and the day by turning the other.

Which movement for which mod?

NH35 is the right call for:

• Submariner-style homages (Sub collection)
• Yacht-Master-style homages (Yacht collection)
• Oyster-Perpetual-style homages without a date window (one NH35 variant can also be set up "dateless" — the date wheel is simply covered)
• Datejust-style homages with date only
• Pilot mods with large-numeral layouts

NH36 is the right call for:

• Day-date homages
• Seiko 5 Sports-style mods (classic day/date at 3 o'clock)
• Classic vintage-style Seiko homages
• Builds where a day-of-week display is specifically wanted

What modders get wrong

Mistake 1: choosing the NH36 for "more features." The day display sounds useful — in practice, hardly anyone actually checks it, since your phone answers that question faster 90% of the time. It also narrows your dial choices significantly: NH35-compatible dials outnumber NH36-compatible ones roughly 5–10x in the modding market.

Mistake 2: fitting an NH35 dial onto an NH36 movement. This doesn't work mechanically — the day wheel physically blocks it.

Mistake 3: buying aftermarket movements without regulation. Both movements ship with a wide accuracy tolerance (-20 to +40 s/day). Without regulation on a timing machine, you might get lucky (5 s/day) or unlucky (35 s/day). On a mod build, the €25–40 for movement regulation is worth it every time.

What does it cost?

• NH35: €50–90 (depending on source, used or new)
• NH36: €70–110
• Movement regulation: €25–40

The upcharge for the NH36 is modest — but only justified if you genuinely want a day-date layout.

Our recommendation

For 90% of mods, the NH35 is the right choice. It's cheaper, has the wider dial selection, remains more common among watchmakers, and fits every mainstream modding platform. Only reach for the NH36 if your dream dial specifically demands a day-date layout.

One more note: the NH34 (the GMT movement) is a different topic entirely — we recommend it for our Sky collection, since it enables a genuine second time zone hand. More on that in our Sky collection guide.