How to Calculate Planetary Hours

Planetary hours are the most practically applicable timing tool from the tradition of Western ceremonial and folk magick. The system divides each day and night into twelve unequal segments, assigning each segment to one of the seven classical planets in a fixed repeating sequence. By knowing which planet rules the current hour, a practitioner can choose the optimal moment for a working within any given day, regardless of which sign the moon occupies or what the broader astrological weather is doing.

The calculation is not difficult. Once you have worked through it once, it takes only a few minutes to determine the planetary hours for any day, and most practitioners either calculate them in advance for the week or use one of the many apps and websites that do the calculation automatically.

History and origins

The planetary hours system is ancient, appearing in Hellenistic astrological literature and in use by the first centuries of the common era. The seven classical planets, Saturn, Jupiter, Mars, Sun, Venus, Mercury, and Moon, were understood as the seven spheres of the cosmos through which souls descended at birth and ascended after death, and their attribution to specific hours encoded the quality of those hours with each planet’s characteristic energy.

The sequence of the days of the week as we know them, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, derives directly from the planetary hours system: the planet ruling the first hour of each day gives that day its name, which has survived in many languages across two millennia. The English days retain the planet names in older forms: Sun’s day, Moon’s day, Tiw’s day (Mars), Woden’s day (Mercury), Thor’s day (Jupiter), Frigg’s day (Venus), Saturn’s day.

Planetary hours appear in medieval Arabic astrological manuals, in Renaissance ceremonial magic texts including those of the Order of the Golden Dawn’s inheritance, and in folk magic traditions that associated specific activities with specific planetary days and hours. They remain one of the most widely used timing systems in contemporary magickal practice.

In practice

A method you can use

Step 1: Find your local sunrise and sunset times. Look up today’s sunrise and sunset times for your location. These are readily available through weather apps, the US Naval Observatory website, or a simple internet search for your city and date. Note both times precisely.

Step 2: Calculate the length of a daytime hour. Subtract the sunrise time from the sunset time to find the total length of daylight. Divide this by twelve. The result is the length of one daytime planetary hour. Example: sunrise at 6:00 AM and sunset at 8:00 PM gives fourteen hours of daylight, divided by twelve gives seventy minutes per daytime planetary hour.

Step 3: Calculate the length of a night hour. Subtract the daytime duration from twenty-four hours to find the night duration. Divide by twelve. In the example above, ten hours of night divided by twelve gives fifty minutes per nighttime planetary hour.

Step 4: Identify the day ruler. The planet ruling the day determines which planet rules the first hour after sunrise. The day rulers are: Sunday = Sun, Monday = Moon, Tuesday = Mars, Wednesday = Mercury, Thursday = Jupiter, Friday = Venus, Saturday = Saturn.

Step 5: Assign planets to hours. Beginning with the day ruler in the first hour after sunrise, continue through the Chaldean order: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon, then repeat from Saturn. The sequence is always the same; only the starting planet changes based on the day.

Example for a Wednesday. Wednesday is ruled by Mercury, so the first daytime hour begins at sunrise with Mercury. The second hour is Moon, the third Saturn, the fourth Jupiter, the fifth Mars, the sixth Sun, the seventh Venus, the eighth Mercury again, and so on through all twelve daytime hours and then the twelve night hours.

Step 6: Calculate the actual clock time of each hour. Starting from sunrise, add the daytime hour length repeatedly to find when each planetary hour begins. If sunrise is 6:00 AM and daytime hours are seventy minutes long, the second hour begins at 7:10 AM, the third at 8:20 AM, and so on through sunset, after which you switch to the shorter night hours.

Applying planetary hours to magickal work

Once you know the planetary hour sequence for your day, choose a working time that aligns with your intention:

Sun hours suit workings of success, recognition, leadership, health, and solar deity devotion. Moon hours suit psychic work, dreams, emotional healing, water-based workings, and lunar devotion. Mars hours suit courage, protection, conflict resolution, physical energy, and competitive situations. Mercury hours suit communication, writing, contracts, travel, divination, and learning. Jupiter hours suit abundance, expansion, legal matters, higher learning, and long-term growth. Venus hours suit love, beauty, pleasure, art, and relationship work. Saturn hours suit binding, limitation, discipline, long-term commitments, and workings that require patience and structure.

Many practitioners combine planetary hour timing with the day’s planetary ruler: performing a Venus working on Friday in a Venus hour concentrates the energy most powerfully. Working on a day whose ruler conflicts with your intention is not necessarily counterproductive, but a supportive hour can compensate for a neutral or unfavourable day ruler.

In myth and popular culture

The planetary hours system has been embedded in Western magical and astrological practice for more than two thousand years and appears prominently in the grimoire tradition. The Key of Solomon, one of the most influential magical texts in European history, specifies planetary hours for virtually every operation it describes: the fashioning of specific tools, the collection of herbs, the performance of particular rituals. The system is presented there not as one option among many but as a foundational requirement for effective magical timing.

In Renaissance literature, awareness of planetary hours was assumed among educated readers. Christopher Marlowe’s Doctor Faustus and other magical dramas of the period reflect a cultural context in which astrological timing for magical operations was a familiar concept, if also a feared and stigmatized one. John Dee, the Elizabethan mathematician, astrologer, and occultist, recorded planetary hours calculations in his diaries alongside his other astrological and magical workings.

The planetary hours system also underpins the modern seven-day week and the names of its days across multiple language families. The connection between the Chaldean order and day names in English (Sunday through Saturday, with Tuesday through Friday bearing Old English names for Mars, Mercury, Jupiter, and Venus) is a surviving piece of ancient astrological cosmology embedded in the most ordinary feature of daily life.

Contemporary practitioners encounter planetary hours through printed almanacs, dedicated smartphone apps, and websites that calculate them automatically for any location and date. This accessibility has significantly increased the use of planetary hour timing in popular witchcraft and ceremonial practice compared to earlier periods when manual calculation was the only option.

Myths and facts

Several misunderstandings about planetary hours circulate among newer practitioners.

• A common belief holds that planetary hours are equal to sixty-minute clock hours. They are not; they are calculated by dividing the period of daylight and the period of darkness each into twelve equal parts, which means their length varies every day through the year and they equal sixty minutes only near the equinoxes.
• Some practitioners assume that planetary hour timing overrides all other considerations. Planetary hours are one factor among several in electional timing; they work alongside the day of the week, lunar phase, moon sign, and broader astrological conditions rather than superseding them.
• Many beginners believe they must calculate planetary hours manually from scratch each day. Numerous apps and websites provide automatic calculations for any location and date; manual calculation is a useful skill to understand but not a daily requirement.
• A widespread misconception holds that planetary hours are a medieval European invention. The system is Hellenistic in origin, documented in ancient astrological texts from the first centuries of the common era, and the day-of-the-week naming system that flows from it predates Christianity in the Roman world.
• Some sources suggest that planetary hours in the Southern Hemisphere should be reversed or corrected. The standard planetary hours calculation does not reverse in the Southern Hemisphere; it follows the same Chaldean order beginning from the day ruler, though some practitioners adapt other astrological directions for Southern Hemisphere practice.