The Tudor Black Bay 36 sits at an unusual inflection point in the mid-range watch market: 36 millimetres from the brand that helped define the purpose-built tool watch, now carrying a full manufacture movement and COSC certification for under $5,000. When Tudor launched the M79640 in July 2025 it replaced the ETA-based T600 calibre of the outgoing M79500 with its own Calibre MT5400 — the same movement family powering the larger Black Bay models — and in doing so built the most credible case yet for buying small.
This guide covers everything a buyer needs to know in 2026: every current M79640 reference, what changed from the M79500, the MT5400 movement explained in full, how the 36mm case wears across different wrist sizes, and what pre-owned pricing looks like for the outgoing generation. Whether you are deciding between this watch and something larger, something older, or something from a different brand, the context is all here.
Quick Verdict
The M79640 Black Bay 36 is the most compelling argument Tudor has made for the 36mm case in years. The MT5400 movement brings COSC certification, a 70-hour power reserve and a silicon balance spring — credentials that justify the step up from the outgoing T600-based model and narrow the credibility gap to the Rolex Explorer 36. The anthracite M79640-0001 is the most versatile reference in the lineup; the blue M79640-0002 is the most dressed. Buy new if you want the manufacture movement; consider a pre-owned M79500 if your budget sits under $3,000 and the ETA calibre is not a dealbreaker.
What Changed in 2025: M79640 vs M79500
The M79640 is not a cosmetic refresh. Tudor made four substantive changes when it replaced the M79500, and each one matters to a buyer comparing the two generations.
Movement. The T600 calibre — a modified ETA movement — gave way to the MT5400, a full manufacture calibre developed entirely in-house by Tudor. The MT5400 is COSC-certified (meaning the movement keeps time within −4/+6 seconds per day), beats at 28,800 vph (4 Hz), and delivers a 70-hour power reserve compared to the T600’s 38 hours. The practical effect of that extra 32 hours of reserve is real for anyone who wears a watch Monday to Friday and rests it over the weekend: the M79640 will typically still be running on Monday morning.
Crystal. The M79500 wore a domed sapphire crystal — one of the visual signatures of the original Black Bay design. The M79640 moves to a flat sapphire crystal, bringing the watch in line with the rest of the current Black Bay range. Reflections at oblique angles are reduced with the flat crystal, though the domed glass had its own period character that some buyers will miss.
Water resistance. The M79500 was rated to 150 metres. The M79640 is rated to 100 metres. For a watch used as a dress-sport hybrid rather than committed diving duty, 100 metres remains more than adequate for swimming and snorkelling. The change is worth flagging because Tudor’s larger Black Bay models are still rated to 200 metres — buyers coming from those pieces will notice the step down.
Price. Retail pricing for the M79640 opens at approximately $4,400 (M79640-0001) versus roughly $3,575 for the outgoing M79500 at its market peak. The premium is real, but the movement upgrade goes a long way toward justifying it over the life of the watch.
Every M79640 Reference Explained
Tudor launched the M79640 in several steel-bracelet configurations, each sharing the same 36mm stainless steel case, MT5400 movement, 100-metre water resistance, and five-link bracelet with Tudor’s T-fit folding clasp. The differences between references come down to dial colour and strap choice.
M79640-0001 — Anthracite Dial
The M79640-0001 pairs an anthracite dial with the five-link steel bracelet. The dark grey tone sits between black and charcoal, taking on different qualities under different light — cool and legible in daylight, warmer under incandescent lighting. Applied baton hour markers and a sword-style seconds hand maintain the traditional Black Bay DNA without leaning too heavily on retro ornamentation. At approximately $4,400 retail, the M79640-0001 is the most versatile reference in the lineup — it dresses up without effort while remaining entirely appropriate in casual settings. This is also the reference most widely stocked by authorised dealers.
M79640-0002 — Blue Dial
The M79640-0002 carries a blue sunburst dial, one of the most-requested colourways across the whole Black Bay collection. The blue shifts with the light in a way the anthracite reference does not, making it slightly more expressive as a dress watch and more visually interesting in formal settings. At approximately $4,725 retail it commands a modest premium over the anthracite, though that figure varies by region and retailer. For buyers who already own a darker-dialled everyday watch and want contrast, the blue is the natural choice.
M79640-0003 — Champagne Dial
The M79640-0003 introduces a champagne or cream dial — a warmer, less common option in the Black Bay 36 lineup. It wears closer to a dress watch than the other references and pairs particularly well on a leather or vintage-inspired strap. The champagne dial suits buyers who want something that works at formal occasions without reaching for a dress watch brand. Pricing is in line with the M79640-0001.
Leather Strap Variants
Each reference is also offered on leather and textile strap configurations, typically at a modest discount versus the bracelet variants. Tudor fits these versions with the same M79640 case and movement. If you plan to run the watch on a NATO or leather strap from day one, the strap variants are worth asking about at your authorised dealer — they are not always prominently displayed in showrooms. The T-fit bracelet clasp also accepts Tudor’s quick-change system, so switching to an aftermarket strap requires no tools.
The MT5400 Movement: Why It Matters
The MT5400 is the centrepiece of the M79640’s upgrade argument, and it delivers on three fronts that matter to practical buyers in this price category.
COSC chronometer certification. The MT5400 passes the Swiss Official Chronometer Testing Institute’s rigorous testing regime: accuracy within −4/+6 seconds per day across five positions and three temperatures. In practice, most MT5400 specimens run well inside ±2 seconds per day. This is not a theoretical headline figure — it is independently verified, batch by batch, before the movement is cased up.
Silicon balance spring. The MT5400 is fitted with a silicon hairspring. Silicon is non-magnetic, corrosion-resistant, and maintains its geometry more consistently than traditional Nivarox alloy across the power reserve arc. The practical upside: better isochronism from full wind to nearly depleted, and no need to demagnetise the watch after passing through airport security equipment or working near electromagnetic fields.
70-hour power reserve. At 28,800 vph (4 Hz), the MT5400 offers a power reserve of approximately 70 hours — nearly three full days. For a watch worn Monday to Friday and left on the nightstand over the weekend, it will typically still be running when you pick it up on Monday morning. For weekend-only wearers, this means less frequent winding than the outgoing T600 required. For a detailed look at Tudor’s long-term ownership picture, see our guide to Tudor ownership costs.
How Does It Wear? The Case in Context
Thirty-six millimetres is a polarising number in contemporary watch culture, where 40mm has become a default. The honest answer is that fit depends less on wrist circumference than most guides suggest and more on the specific proportions of a case at that diameter.
The Black Bay 36’s lugs are relatively short, keeping the watch compact on the wrist relative to its diameter. The domed bezel adds visual presence beyond what the flat measurement conveys, and the applied markers and sword hands give the dial a three-dimensionality that photographs struggle to capture. The result is a watch that reads as more present on the wrist than a quick glance at the case size would imply.
For wrists under approximately 17cm in circumference, the BB36 is likely the best-fitting watch in the Black Bay range. It does not look miniaturised; it looks correctly proportioned. For larger wrists, the watch still wears well — it simply reads as an intentional choice rather than the default. The BB36 versus Rolex Explorer (2026) comparison gives a detailed side-by-side of how both 36mm watches sit across different proportions.
The M79500 Pre-Owned Case
The outgoing M79500, powered by the T600 movement, is now available on the pre-owned market at prices typically between $2,200 and $2,800 depending on condition and whether box and papers are included. Here is the honest case for and against.
For the M79500: The T600 calibre is a well-proven, robustly serviceable movement — ETA-based calibres are serviced by watchmakers all over the world without specialist parts. The 150-metre water resistance rating exceeds the M79640’s 100 metres. The domed sapphire crystal is characterful and visually distinctive. And the price difference is significant: buying a pre-owned M79500 saves roughly $1,500–$2,200 versus a new M79640.
Against the M79500: You are buying a discontinued watch with no manufacture movement credentials. The MT5400 is genuinely superior to the T600 in power reserve and silicon hairspring technology. The 38-hour reserve requires more regular winding for weekend-only wearers. And pre-owned availability will narrow over time as the M79500 moves further into collector territory.
For buyers on a strict budget under $3,000 who want the classic Black Bay 36 experience, the pre-owned M79500 is a sensible purchase. For buyers who want the full manufacture story at the smallest Black Bay case size and are comfortable paying closer to new retail pricing, the M79640 is the better long-term proposition.
Who Should Buy the Tudor Black Bay 36?
The M79640 Black Bay 36 makes sense for a specific buyer, and it is worth being direct about that.
This watch is the right choice if: you find 40mm and above too large for your wrist or lifestyle; you want a manufacture-calibre movement under $5,000; you want a watch that moves equally well from a business meeting to a weekend trip; or you want something from a heritage brand with manufacture credentials that is not on a waiting list or subject to dealer favouritism. The BB36 is not allocated — you can walk into an authorised dealer and buy one.
Look elsewhere if: you need dive-rated water resistance above 100 metres; you are searching for the ideal 38–40mm range; or you want the cheapest possible entry point to the Black Bay aesthetic — in that case the pre-owned M79500 is worth considering first. The Tudor Black Bay 36 review covers the wearing experience in more detail for buyers who want to go deeper before making a decision.
The M79640 (launched July 2025) replaces the M79500 with Tudor’s in-house Calibre MT5400 movement — COSC-certified, 70-hour power reserve, silicon balance spring — versus the ETA-based T600 of the M79500 with 38 hours reserve. The M79640 also moves to a flat sapphire crystal from the M79500’s domed sapphire, and the water resistance rating changes from 150 metres to 100 metres. Retail pricing for the M79640 starts at approximately $4,400 versus roughly $3,575 for the M79500 at its peak.
Yes. All current M79640 references are available on Tudor’s five-link steel bracelet, fitted with the T-fit folding clasp that includes a push-button micro-adjustment. The bracelet is removable via Tudor’s tool-free quick-change system, allowing strap swaps without visiting a watchmaker. Leather and textile strap variants of the same M79640 references are also available through authorised dealers.
The Tudor Black Bay 36 M79640-0001 (anthracite dial) retails at approximately $4,400 USD. The M79640-0002 (blue dial) retails at approximately $4,725 USD. The M79640-0003 (champagne dial) is similarly priced to the anthracite reference. Pre-owned examples of the outgoing M79500 generation are available from approximately $2,200–$2,800 depending on condition and whether box and papers are present.
Yes — the M79640 generation uses Tudor’s Manufacture Calibre MT5400, developed entirely in-house. The MT5400 is COSC-certified, beats at 28,800 vph (4 Hz), offers approximately 70 hours of power reserve, and uses a silicon balance spring for improved anti-magnetic resistance and isochronism. The outgoing M79500 used the T600 calibre, which was based on an ETA ebauche and is not an in-house movement.
Both watches share the 36mm case diameter, but differ significantly in movement credentials, price and provenance. The Rolex Explorer uses the Calibre 3230 — an impressively thin in-house movement with COSC certification and 70 hours of power reserve, similar to the Tudor’s MT5400. The Explorer retails at roughly twice the price of the Black Bay 36 and is subject to availability constraints at authorised dealers. The Tudor is freely available new, carries broadly comparable movement credentials, and costs approximately half as much. For a detailed comparison see our Black Bay 36 vs Rolex Explorer guide.
The Tudor Black Bay 36 M79640 is a rarer thing than it might appear in this category: a 36mm watch from a heritage brand with an in-house certified movement, available in multiple colourways, without a waiting list or allocation hurdle. The upgrade from the M79500 is substantive rather than cosmetic, and the retail premium is easier to justify in 2026 than it would have been a few years earlier when the ETA-era pricing looked more competitive. If you are shopping in this segment, the M79640 earns a first appointment with an authorised dealer.
