The IWC Portugieser Eternal Calendar IW505701 is a secular perpetual calendar: its 400-year gear accounts for Gregorian century-year exceptions that a conventional four-year calendar would miss. IWC says the gear skips the leap days in 2100, 2200 and 2300, and that the calendar calculates correctly through at least 3999. Separately, IWC says the Double Moon display’s calculated deviation from the moon’s orbit reaches one day after 45 million years; that is a moon-phase claim, not the watch’s rate accuracy.
Unveiled in April 2024, the platinum Portugieser pairs the calendar with automatic Calibre 52640, a seven-day power reserve and a transparent glass-dial architecture. IWC lists its diameter as 44.4 mm and its height as 14.9 mm. The specifications and performance figures below are manufacturer-reported, not independently tested.
What makes the IWC Eternal Calendar different?
A conventional perpetual calendar generally follows a four-year pattern, adding February 29 every fourth year. The Gregorian calendar adds an exception: years divisible by 100 are common years unless they are also divisible by 400. That makes 2000 and 2400 leap years, but 2100, 2200 and 2300 common years.
| Year | Gregorian result | Why it matters mechanically |
|---|---|---|
| 2000 | Leap year | It is divisible by 400. |
| 2100 | Not a leap year | A four-year-only calendar would expect February 29. |
| 2200 | Not a leap year | The century exception occurs again. |
| 2300 | Not a leap year | The mechanism must skip another expected leap day. |
| 2400 | Leap year | It is divisible by 400. |
IWC says the IW505701 adds a 400-year gear that makes one revolution per four centuries. Three indentations in that gear cause the calendar to skip the three leap years that are not leap years under the Gregorian rule. A conventional four-year-only mechanism needs correction at those century exceptions; this mechanism encodes them in its cycle.
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That is why secular perpetual calendar is the more precise description. IWC says the calendar calculates correctly until at least 3999 and notes that the status of year 4000 has not been officially decided. The 400-year cycle describes the encoded calendar rule; it is not a guarantee that the watch can operate forever without service.
IWC Portugieser Eternal Calendar IW505701: specifications
| Specification | IWC-listed detail |
|---|---|
| Reference | IW505701 |
| Case material | Platinum |
| Dial | White |
| Diameter and height | 44.4 mm diameter; 14.9 mm height |
| Movement | Automatic IWC-manufactured Calibre 52640 |
| Power reserve | 168 hours (seven days) |
| Frequency | 28,800 vibrations per hour (4 Hz) |
| Components and jewels | 396 components; 54 jewels |
| Displays | Day, date, month, four-digit year and eternal moon phase |
| Water resistance | 5 bar |
| Strap | Black Santoni alligator leather, 22 mm wide |
These dimensions are IWC’s current listed specifications for IW505701. They provide a size reference, but do not establish how the watch will fit or feel on any particular wrist.
Inside Calibre 52640
IWC says all calendar displays can be advanced using the crown. Calibre 52640 is automatic and uses Pellaton winding, with two barrels providing the stated 168-hour reserve. The seven-day figure is the manufacturer’s stated running time from a full wind, not a promise that the watch can be left unattended indefinitely.
IWC says the winding system uses ceramic components in highly stressed parts. The transparent caseback makes the movement visible. These construction details come from IWC’s launch materials and are not an independent assessment of long-term reliability.
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What the seven-day reserve does—and does not—mean
A seven-day reserve means the watch can run for a week from a full wind under the manufacturer’s stated specification. If it stops, it will need to be set or advanced again according to IWC’s operating instructions. A watch winder is an optional storage convenience, not a requirement established by the movement specification.
A transparent Portugieser design
The watch’s glass dial and sapphire sub-dials create a layered, open presentation. IWC describes the dial as glass with white printing on its underside, and lists double box-glass sapphire crystals with antireflective coating on both sides. The transparent caseback continues that presentation from the front to the rear.
Applied Arabic numerals, leaf-shaped hands and a railway-track minute scale retain recognizable Portugieser design cues. The large case and open dial may make the composition appear visually airy, but that does not show that a 44.4 mm platinum watch will wear small or feel light on a particular wrist.
The Double Moon display
The Double Moon display represents the moon phase for both the Northern and Southern Hemispheres. It is separate from the 400-year calendar gear: that gear handles Gregorian leap-year exceptions, while the Double Moon indication concerns the moon’s cycle.
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IWC says the display will mathematically deviate from the moon’s orbit by one day after 45 million years. IWC’s launch release gives the lunation used in its explanation as 29 days, 12 hours, 44 minutes and 2.88 seconds. It also says the gear train uses three intermediate wheels after evaluating more than 22 trillion combinations. These are IWC’s reported design and calculation figures, not independently verified test results. The 45-million-year figure is not the watch’s timekeeping rate accuracy or a practical ownership interval.
Video: what to watch for
IWC unveiled the IW505701 in April 2024 as part of its new Portugieser collection. Its official launch material presents the secular calendar, Double Moon claim, platinum case and transparent construction. Assembly footage can offer visual context for how the movement is put together, but should be treated as an official manufacturing presentation, not independent evidence of reliability or tested performance.
Recognition and significance
IWC’s product page reports that the Eternal Calendar won the Grand Prix de l’Aiguille d’Or at the 24th Grand Prix d’Horlogerie de Genève. That is useful context for the watch’s recognition, not proof that it is superior to every competing calendar watch. Its specific distinction is the 400-year mechanism combined with a Portugieser design and open dial presentation.
Who is the IW505701 for?
- For the calendar specialist: Its 400-year gear encodes the Gregorian century-year exceptions that a four-year-only calendar misses.
- For the movement enthusiast: Calibre 52640 combines automatic Pellaton winding, two barrels and a stated seven-day reserve.
- For the design collector: The glass dial, sapphire sub-dials and transparent caseback make the movement part of the presentation.
- For the traditional dress-watch buyer: Portugieser design cues remain, but the 44.4 mm platinum case is substantial on paper; dimensions alone cannot predict fit.
If the goal is simply to know the date with minimum fuss, a simpler watch or phone is more practical. The IW505701 is aimed at collectors interested in the mechanical solution, its calendar display and the way its complication is presented.
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Availability, price and ownership notes
IWC’s product page offers inquiry and appointment options, but the supplied research does not verify a current public price, live availability or a numbered limited-edition status. Confirm price, delivery terms and availability with IWC for the relevant market rather than relying on an unsourced figure.
IWC’s product page says registration in My IWC Care while the original warranty is active can extend the standard two-year international limited warranty by six years, to eight years total. Warranty terms and eligibility should be checked against the current local terms before purchase.
Verdict
The IW505701’s defining feature is the 400-year gear that encodes Gregorian century-year exceptions. IWC says it skips the leap days in 2100, 2200 and 2300 and calculates correctly through at least 3999. That is the substance behind the “Eternal Calendar” name—not a promise of operation forever without service.
The separate Double Moon display adds IWC’s theoretical one-day-after-45-million-years deviation claim; Calibre 52640 supplies automatic winding and a seven-day reserve. The trade-offs include a 44.4 mm by 14.9 mm platinum case and 5 bar water resistance. For a collector drawn to calendar mechanics and the transparent presentation, this is a technically ambitious Portugieser, rather than a practical necessity.
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FAQ
How does the 400-year calendar work?
IWC says a gear makes one revolution per four centuries and has three indentations that make the calendar skip the non-leap century years 2100, 2200 and 2300. The Gregorian rule makes century years leap years only when divisible by 400.
Is the Double Moon’s 45-million-year figure the watch’s accuracy?
No. IWC’s figure describes the calculated deviation of the moon-phase display from the moon’s orbit. It is not the rate accuracy of the watch.
How long is the Calibre 52640 power reserve?
IWC lists a 168-hour, or seven-day, power reserve for the automatic Calibre 52640.
What are the IW505701’s case dimensions?
IWC lists a 44.4 mm diameter and 14.9 mm height. Those measurements do not determine how the watch will fit an individual wrist.
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