NH35 vs NH36: Which Seiko Mod Movement Should You Use? (2026)
If you're building a Seiko mod, two movements come up more than any others: the NH35 and the NH36. They look nearly identical, they cost about the same, and they drop into the same cases — so what's the actual difference, and which one should you use? I've built with both plenty of times, so here's the clear version.
The short answer
The difference is one complication: the NH35 shows the date only. The NH36 shows the day and the date. That's the headline. Everything else — the automatic winding, the reliability, the size, the price — is essentially the same. If you want a clean dial with just a date window, use the NH35. If you want the day of the week spelled out too, use the NH36. Now here's the detail that actually matters when you're building.
The NH35 — date only (the modding default)
The NH35 is the workhorse of the Seiko modding world, and for good reason. It's a genuine Seiko automatic (made by Seiko Instruments, the same group behind the movements in Seiko's own entry watches), it hacks (the seconds hand stops when you pull the crown, so you can set the time precisely), it hand-winds, and it runs at 21,600 beats per hour with roughly 41 hours of power reserve on a full wind.
Its defining feature for modders is simplicity: a single date window. That gives you a cleaner dial and the widest possible choice of aftermarket dials, because almost every mod dial is cut for a date-only movement. If you're not sure which to pick, the NH35 is the safe default — it's what most of our prebuilt Royal Oak mods run.
The NH36 — day-date (when you want the day of the week)
The NH36 is the NH35's twin with one extra trick: a day-date complication. Alongside the date, a second window (usually at 3 o'clock, above or beside the date) displays the day of the week — and on most versions you can toggle the day language between English and a second language. Everything else is identical: same automatic winding, same hacking and hand-winding, same 21,600 bph, same ~41-hour reserve, same physical dimensions.
The catch: because it drives a day wheel, the NH36 needs a dial cut for day-date. A standard date-only mod dial won't show the day window correctly. So if you want the NH36's day complication, plan your dial around it from the start.
Side by side
| Spec | NH35 | NH36 |
| Complication | Date only | Day + date |
| Winding | Automatic + hand-wind | Automatic + hand-wind |
| Hacking (stop-seconds) | Yes | Yes |
| Beat rate | 21,600 bph | 21,600 bph |
| Power reserve | ~41 hours | ~41 hours |
| Jewels | 24 | 24 |
| Dial requirement | Date-only (most dials) | Day-date dial |
| Best for | Clean, versatile builds | Builds that want day-of-week |
Which should you use for your mod?
Simple rule of thumb:
- Choose the NH35 if you want a clean dial, the maximum choice of aftermarket dials, and you don't care about seeing the day of the week. This covers the vast majority of builds — it's the default for a reason.
- Choose the NH36 if the day-date is a feature you actually want (some people love it, some find it cluttered) and you're pairing it with a dial made for day-date.
One more thing worth knowing: neither of these is a "better" movement — they're the same movement with a different calendar. Don't overthink it. Pick based on the dial and the complication you want, not on some imagined quality difference.
Where the rest of the NH family fits
The NH3x series is bigger than just these two, and the others solve different jobs. Quick tour so you know your options:
- NH34 — adds a GMT (second time-zone) hand. For dual-time builds.
- NH38 — no date, with an open-heart cutout, for dials that show the balance wheel.
- NH70 / NH71 / NH72 — the skeleton movements, finished to be seen through an open-worked dial. The NH72 in particular is what we use in our skeleton Royal Oak and Nautilus builds — same reliable base, dressed up to be on display.
All of them share the same mounting and dimensions as the NH35/NH36, so they generally drop into the same cases — you're mostly choosing based on the complication and whether you want the movement hidden or on show.
Compatibility — do they fit the same cases and dials?
Cases: yes. The NH35, NH36, and the rest of the NH3x family share the same movement dimensions, so a case built for one fits the others. Dials: mostly — the difference is the calendar window. A date-only dial works with an NH35; a day-date build needs a day-date dial. Always match the dial to the movement's calendar, and check the dial size (28.5 mm or 30.8 mm) for your specific case before ordering. Our build guide walks through fitting the movement step by step.
Frequently asked questions
Is the NH36 more accurate than the NH35?
No — they're the same base movement and run to the same accuracy (typically around -20 to +40 seconds/day out of the box, and better once regulated). The only difference is the day complication.
Can I swap an NH35 for an NH36 in an existing mod?
Physically yes — they're the same size and mount the same way. But you'd also need a dial cut for day-date to actually use the day window, so it's not a drop-in for the calendar unless your dial already supports it.
Which movement does Seiko use in its own watches?
Seiko's branded equivalents are the 4R35 (date) and 4R36 (day-date) — mechanically the same as the NH35 and NH36. The "NH" designation is just the version Seiko Instruments sells to the modding and micro-brand market.
Do they hand-wind and hack?
Yes, both. You can wind them manually via the crown and the seconds hand stops when you pull the crown out to set the time — two features the older 7S26 lacked, and a big reason the NH3x series is the modding standard.
The bottom line
NH35 for a clean date-only build with the widest dial choice; NH36 when you specifically want the day of the week and have a dial to match. Same reliability, same price ballpark, same everything else. If you're just getting started, go NH35 — you can always build something with a day-date later. Have a look at the full movement range when you're ready to pick one.
