Kosei
Boys' nameMeaning not yet documented
Kosei has been given to 90 babies in the U.S. since 2000. It was used fewer than 5 times in 2025, so it doesn't appear in the latest year's list — today it's a genuinely uncommon pick. Its peak year was 2008, with 9 recorded.
Babies named Kosei, 2020
1 in 477,000
Kosei over time, 1880–2025
Based on births in the U.S. Babies given the name each year. Hover the chart — or focus it and use the arrow keys — for any year. Gaps mean the name was given fewer than 5 times that year; these counts are unpublished.
How common is Kosei?
Kosei had fewer than 5 recorded uses in 2025, so these figures use 2020, the last year it was published.
- Among all babies, 2020
- 1 in 477,000
- 7 of 3,342,313 births
- Among boys only
- 1 in 247,000
- <0.01% of boys
- Rank, 2020
- Unranked
- Fewer than 5 uses
- Coin-flip room size
- 330,960 kids
- Even odds of a second one
Where Kosei sits on the popularity scale
Chance at least one other child shares the name
If the other children were drawn at random from the 2020 national name distribution. Real classrooms cluster by region and community, so treat these as a floor, not a ceiling.
Put another way: gather 330,960 children born in 2020 and it's an even bet that one of them is another Kosei. In a class of 30 the chance is Under 1%.
When Koseis were born
Half of everyone ever recorded as Kosei was born before 2010 — so the typical Kosei is around 15 today.
- Biggest decade
- 2010s
- 47.8% of all use
- Born in the last 25 years
- 100.0%
- A modern name
- Recorded since 1950
- 90
- People you could plausibly meet
2010s — 47.8% of all recorded uses (43).
Is Kosei rising or falling?
Rank movement and count movement can disagree — the number of distinct names in use keeps growing, so a name holding a steady count still slides down the list. Both are shown.
- Rank vs 1 year ago
- —
- Not ranked then
- Rank vs 5 years ago
- New entry
- Not ranked then
- Rank vs 10 years ago
- —
- Not ranked then
- Births vs 10 years ago
- —
- Not published both years
- Share of its own peak
- 0%
- Peak was 2008 (9)
- Years since peak
- 17
- Years
- Year-to-year steadiness
- Shifting
- 14.3% average annual change
Spellings of Kosei
Kosei is not the most common spelling — Jose is, with 76.5% against Kosei's 0.01%.
Grouped by closeness of spelling (up to two letter changes), same sex, with a floor on all-time use. It catches Sophia/Sofia and Aiden/Ayden, and misses spellings that sound alike but look different, like Sean and Shawn.
Kosei around the world
Where Kosei ranks in official birth records elsewhere in the world. Rankings only — the number of births isn’t comparable between places, so it isn’t shown.
- South Australia2010–2010#754in 2010
Popularity data from Consumer and Business Services (South Australia). CBS SA data under CC BY 4.0.
Kosei by the numbers
The raw record for each sex the name is used for.
Names similar to Kosei
Matched on shared beginnings and endings, similar length, and comparable popularity.
Sibling names for Kosei
Names from the same era and popularity tier — the two things that make a sibling set feel deliberate — skipping lookalike spellings and shared initials.