What's the difference between "60세" and "만 60세"?

 ANSWER: One means 60 years old, and the other means Korean-age 60 years old, which is really 59 years old.

The Chinese character 歲 (세) is the same 세 used in the Sino-Korean word 연세 (年歲), which means "age" or "years of age." When Koreans say "60세," they are referring to the Korean style of counting "years of age," which means an extra year is added because when Koreans are born, they are already considered to be 1 year old. In the United States, we are 1 year old only after one year of being born. So, 60세 would mean "59 years old" in countries like the United States. When Koreans want to refer to 60 years old in the Western way, they say, "만 60세." The Chinese character 滿 (만) means "full," so 만 60세 literally means "a full 60 years old."

In Korea, the word 환갑 (還甲) refers to "one's 60th birthday anniversary." But does "60th birthday" means "60세" or "만 60세"? In other words, does 환갑 refer to Korean-age 60 or Western-age 60?

ANSWER: It refers to Western-age 60 ("만 60세), which again means that it is referring to "a full 60 years old." I will explain why below.

Why does 환갑 refer to "a full 60 years old" (만 60세) instead of a "Korean 60 years old" (60세)? Because 환갑 (還甲) literally means "returning to (還) 갑 (甲)," and 갑 (甲) is referring to the first of ten "heavenly stems" (천간 天干) in the "sexagenary cycle" (육십갑자 六十甲子), which counts years in 60-year cycles by combining, in sequence, one of ten "heavenly stems" (천간 天干) with one of twelve "earthly branches" (지지 地支). A "heavenly stem" is the first character in the 2-character combination, and an "earthly branch" is the second character. If you multiply 10 (heavenly stems) by 12 (earthly branches), you get 120, which means one could make 120 different 2-character combinations out of the 10 heavenly steams and 12 earthly branches, but since a "heavenly-stem" character can only appear as the first character in the 2-character combinations and an "earthly-branch" character as the second in the combinations, we have to divide the 120 by 2, which gives us only 60 possible unique character combinations for the different year names in a 60-year cycle.

The first year in a 60-year cycle is called 갑자 (甲子), which combines the "heavenly stem" 甲 (갑) with the "earthly branch" 子 (자), so instead of saying "환갑" (還甲), it would be more accurate to say "환갑자" (還甲子) since you "return to" (還)  a 갑 (甲) year on year 11 (갑술 甲戌), year 21 (갑신 甲申), year 31 (갑오 甲午), year 41 (갑진 甲辰), and year 51 (갑인 甲寅) before returning to year 1 of a new 60-year cycle. However, you "return to" (환 還) a 갑자 (甲子) combination only on year 1 of a new 60-year cycle, and that means that 환갑 (還甲) is referring to a "full" (만 滿) 60-year cycle. And that means that each year in a 60-year cycle will have its own unique name.

Below is a chart showing the 10 "heavenly stems" (천간) above the 12 "earthly branches" (지지). The name of the first year of the 60-year cycle is a pairing up of the first "heavenly stem" (甲 갑) with the first "earthly branch" (子 자), so 甲子 (갑자); and the name of the second year is a pairing up of the second "heavenly stem" (乙 을) with the second "earthly branch" (丑 축), so 乙丑 (을축); and so-on through year 10, after which we run out of "heavenly stems" and must return to the beginning of the "heavenly stems" to continue the pairing, so the name of the 11th year in the 60-year cycle is a pairing of the first "heavenly stem" (甲 갑) with the 11th "earthly branch" (戌 술) to form 甲戌 (갑술). And then continuing in sequence, the name of the 12th year in the 60-year cycle is a pairing of the second "heavenly stem" (乙 을) with the 12th earthly stem (亥 해) to form 乙亥 (을해). After that, there are no more "earthly branches," so we must start repeating the "earthly branches" to continue naming the remaining years of the 60-year cycle. That means that the name of the 13th year  in the 60-year cycle is a pairing of the 3rd "heavenly stem" (丙 병) with the 1st "earthly branch" (子 자) to form 丙子 (병자), and this kind of sequential pairing continues until there is a name for all 60 years in a cycle, after which the first "heavenly stem" (甲 갑) and the first "earthly branch" (子 자) finally meet again to form 甲子 (갑자), the first year of a new 60-year cycle. 

Heavenly Stems 십간

甲 갑

乙 을

丙 병

丁 정

戊 무

己 기

庚 경

辛 신

壬 임

癸 계

甲 갑

乙 을

Earthly Branches 십이지

子 자 rat

丑 축 ox

寅 인 tiger

卯 묘 rabbit

辰 진 dragon

巳 사 snake

午 오 horse

未 미 goat

申 신 monkey

酉 유 rooster

戌 술 dog

亥 해 pig

Year Names

1 甲子 갑자

2 乙丑 을축

3 丙寅 병인

4 丁卯 정묘

5 戊辰 무진

6 己巳 기사

7 庚午 경오

8 辛未 신미

9 壬申 임신

10 癸酉 계유

11 甲戌 갑술

12 乙亥 을해

By the way, each of the "earthly branches" are associated with an animal, so since the "earthly branch" 子 (자) is associated with a "rat," any year that ends with the character 子 is called "the year of the rat." If the name of a year ends with 丑 (축), which is associated with an "ox," then the year would be called "the year of the ox," and so on. And since 子 (자) will appear at the end of a year name 5 times in one 60-year cycle, there will be five "years of the rat" in one 60-year cycle, and there will be five years for each of the other animals, as well.

So, finally, someone celebrating 환갑 (還甲) would be "a full 60 years old" (만 60세), which means he or she would be 61 (61세) Korean age.