How Hoang Ốc is calculated
Of the three taboos Vietnamese families check before breaking ground on a house, Hoang Ốc is the one most often explained away rather than explained. Most write-ups list the names of the six positions, call the method complicated, then print a table of affected ages without saying where the table came from. This article does the opposite: it gives the actual count, so you can redo it on paper and check any table against it.
The six positions
Hoang Ốc sorts every age into six positions, remembered through a rhyme that fixes their order: first Cát, second Nghi, third Địa Sát, fourth Tấn Tài, fifth Thọ Tử, sixth Hoang Ốc. The number before each name is that position's place in the counting cycle.
Three are considered favourable: Nhất Cát, a settled home and smooth affairs; Nhì Nghi, a thriving household; and Tứ Tấn Tài, whose name means fortune arriving.
Three are considered unfavourable: Tam Địa Sát, linked in folk belief to illness; Ngũ Thọ Tử, the most avoided, associated with separation and loss; and Lục Hoang Ốc itself, literally an empty house and thwarted plans.
To be clear from the outset: these are folk readings, not forecasts. The names sound heavy, but the calculation is a six-step count on a single age number.
Counted on lunar age, not Gregorian age
Hoang Ốc reads lunar age: the build year minus the birth year, plus one. Someone born in 1990 is lunar age 37 in 2026, even before their Gregorian birthday.
This is where self-checks most often go wrong. Using the Gregorian age shifts you by one, and because the cycle is only six steps long, one step moves you to a different position entirely, turning favourable into unfavourable or the reverse.
The traditional count: tens first, then units
The cycle starts at age 10, not age 1. The decade marks fall as follows: 10 at Nhất Cát, 20 at Nhì Nghi, 30 at Tam Địa Sát, 40 at Tứ Tấn Tài, 50 at Ngũ Thọ Tử, 60 at Lục Hoang Ốc, then 70 back to Nhất Cát and 80 to Nhì Nghi.
From your decade mark, count on by the units digit, one position per step, wrapping back to Nhất Cát after Lục Hoang Ốc.
Take age 37. The decade is 30, starting at Tam Địa Sát. Counting on seven steps gives 31 Tứ Tấn Tài, 32 Ngũ Thọ Tử, 33 Lục Hoang Ốc, 34 Nhất Cát, 35 Nhì Nghi, 36 Tam Địa Sát, 37 Tứ Tấn Tài. So 37 lands on a favourable position and is not affected.
Take age 23. The decade is 20, starting at Nhì Nghi. Three steps on gives 21 Tam Địa Sát, 22 Tứ Tấn Tài, 23 Ngũ Thọ Tử, an unfavourable position.
The digit-sum shortcut is the same arithmetic
Some texts teach a shortcut: add the two digits of your lunar age, divide by six, and read the remainder as the position number, with a clean division meaning Lục Hoang Ốc.
This is sometimes presented as a rival school giving different answers. It is not. The two are the same expression written two ways: the digit sum of a two-digit age is exactly its tens plus its units, which is how many steps the traditional count takes from the first position. Checking age 37 with the shortcut gives 3 plus 7 equals 10, remainder 4, Tứ Tấn Tài, matching the count above.
The two only diverge from age 100 upward, where the digit sum is no longer tens plus units. Nobody builds a house at that age, so in practice either works. The traditional count has one advantage: it shows the intermediate steps, making a miscount easy to spot.
The affected ages
Applying the count from age 10 to 75, the ages landing on the three unfavourable positions are 12, 14, 15, 18, 21, 23, 24, 27, 29, 30, 32, 33, 36, 38, 39, 41, 42, 45, 47, 48, 50, 51, 54, 56, 57, 60, 63, 65, 66, 69, 72, 74 and 75.
This is not a list to memorise but a result you can rebuild. If another source prints a different list, count a few ages yourself to see which side slipped, rather than trusting whichever looks more familiar.
Hoang Ốc alone is not the whole picture
Hoang Ốc is one of three taboos. The others are Kim Lâu, found by dividing lunar age by nine and reading the remainder, and Tam Tai, read from the trine of your birth-year animal. An age can be clear of one and caught by another.
In practice a year clear of all three is hard to find, especially during someone's three Tam Tai years. Families commonly proceed when only one applies, most often by borrowing an age: asking someone unaffected that year to perform the groundbreaking and roof-raising rituals on their behalf.
How to read Hoang Ốc
Hoang Ốc is a six-step count on an age number. It uses no heavenly stems, no five-element analysis, no birth chart, and distinguishes nobody from anybody else except by year of birth. Everyone born in the same year gets the same answer.
That does not make the custom worthless, but it places it correctly: a shared convention that gave a community one way to time an important undertaking, not a private reading for one household. Understanding what it actually is lets you keep what is good about the custom without letting it drive expensive decisions.
