Head to head · Boys' names
Isaias vs Tadeo
#426 vs #427 in 2025
Isaias is a whisker ahead (#426 vs #427 in 2025), but the curves point different ways: Isaias is holding its place on the charts, Tadeo is climbing the charts fast. On momentum, Tadeo has the edge.
Cast your vote
Which one would you pick?
Your gut first, the numbers after — the split shows once you pick.
The tale of the tape
On the charts, Isaias leads 4 measures of 6; Tadeo leads 2.
Ranks, counts and years are measured in the official US birth record; the classroom and living figures are estimates computed from it. The dot marks the side each measure favours on the charts — more common, not better.
What the records say
146 years of US births, drawn on one scale
Two curves, one scale
Who owned which decade
- 1910s: Isaias #3558, Tadeo — — Isaias higher
- 1920s: Isaias #2769, Tadeo — — Isaias higher
- 1930s: Isaias #1968, Tadeo — — Isaias higher
- 1940s: Isaias #1942, Tadeo — — Isaias higher
- 1950s: Isaias #1664, Tadeo — — Isaias higher
- 1960s: Isaias #1620, Tadeo #4136 — Isaias higher
- 1970s: Isaias #1236, Tadeo — — Isaias higher
- 1980s: Isaias #931, Tadeo #6081 — Isaias higher
- 1990s: Isaias #702, Tadeo #7023 — Isaias higher
- 2000s: Isaias #525, Tadeo #3306 — Isaias higher
- 2010s: Isaias #527, Tadeo #1229 — Isaias higher
- 2020s: Isaias #456, Tadeo #522 — Isaias higher
Isaias stood higher in every recorded decade — 12 of 12.
Rank by decade
| Decade | Isaias | Tadeo |
|---|---|---|
| 1910s | #3558 | — |
| 1920s | #2769 | — |
| 1930s | #1968 | — |
| 1940s | #1942 | — |
| 1950s | #1664 | — |
| 1960s | #1620 | #4136 |
| 1970s | #1236 | — |
| 1980s | #931 | #6081 |
| 1990s | #702 | #7023 |
| 2000s | #525 | #3306 |
| 2010s | #527 | #1229 |
| 2020s | #456 | #522 |
Average national rank across each decade. A dash means the name sat outside the recorded top of that decade.
The names themselves
Meaning, roots, sound and the people who carried each
Where each name comes from
Isaias
Yahweh is salvation
From Hebrew Yesha'yahu, joining the verb for saving with a short form of the divine name.
Yesha'yahu → Ēsaias → Isaias → Isaías → Isaiah
How it traveled
The name belongs first to the Hebrew prophet whose book stands among the longest in the Bible. When Jewish scholars in Alexandria translated those scriptures into Greek, Yesha'yahu became Ēsaias; Latin took it as Isaias, and that is the spelling Jerome used in the Vulgate and English Catholics used for centuries.
Tadeo
Debated — either "heart" or a short form of a Greek name meaning "gift of God"
Two serious readings compete. One traces Greek Thaddaios to an Aramaic root connected with the breast or heart. The other treats it as a Greek pet form of a name like Theodoros or Theodotos, both built on the idea of a gift from God. Neither has won, and the ancient sources do not settle it.
Thaddaios → Thaddaeus → Taddeo → Tadeo
How it traveled
The name begins as Greek Thaddaios, the byname given to one of the twelve apostles — the figure called Thaddaeus in Matthew and Mark, and known in Spanish as San Judas Tadeo. Latin took it as Thaddaeus, and from there each language reshaped it: Taddeo in Italy, Tadeusz in Poland, Tadeo in Spanish.
Where a reading is contested the note says so — this page does not turn a guess into a fact. The chain is each name's recorded forms, oldest first; the story is its opening, told in full on the name's own page.
Out loud, and in short
Isaias
ee-sah-EE-as
That is the Spanish and Portuguese pronunciation, four syllables with the stress on the third. English speakers who read it as a version of Isaiah tend to say eye-ZAY-us, and both are heard in the US.
- Isa — The usual informal shortening in Spanish-speaking families; also stands alone as a given name in several languages.
- Izzy — English-language short form, shared with Isaiah, Isabel and Isabella; casual rather than formal.
- Zay — Informal, used mostly by younger speakers in English; shared with Isaiah and Xavier.
- Chai — Occasional playground clipping of the middle syllables; strictly informal.
Tadeo
tah-DEH-oh
Stress on the middle syllable in Spanish. English speakers who meet it cold sometimes try TAD-ee-oh; one correction usually fixes it, since every letter is doing the job it looks like it is doing.
- Teo — The most natural short form in Spanish, and a standalone given name in its own right.
- Tadeito — Spanish diminutive, used affectionately within families rather than at school.
- Tad — The English-language clipping, shared with Thaddeus; used more by English speakers than Spanish ones.
- Tade — An informal two-syllable trim heard among Spanish speakers.
Is it right for you
The differences that decide it, laid out by what you want
Choose by what you want
Choose Isaias if you want…
- a name holding steadyIsaias is holding its place on the charts
- a name with more sound in itIsaias runs 3 syllables, Tadeo 2
Choose Tadeo if you want…
- a name on the way upup 275 places on the charts in five years
- a name with fewer syllablesTadeo is 2 syllables to Isaias's 3
Each line is a measured difference between the two names — a rank, a count, a recorded form — never a judgement of either. Save the one that answers your question; it lands on your shortlist.
The trade-offs, name by name
Isaias
Strengths
- Works unchanged in Spanish, Portuguese and Latin, and is recognizable in English through its close cousin Isaiah.
- A documented written record stretching back to ancient translations of the Hebrew Bible — the spelling is old, not modern.
- Established short forms already in circulation: Isa, Izzy, Zay.
To consider
- Two live pronunciations compete in the US — the Spanish ee-sah-EE-as and the anglicized eye-ZAY-us. A child will spend some time correcting people, and may end up answering to both.
- The accent in Isaías tends to fall off in American paperwork, school rosters and email systems, which quietly nudges the pronunciation toward the English one.
- It sits close to Isaiah and to Isaí, and gets mistaken for both in writing. Worth deciding early which spelling goes on the birth certificate and holding to it.
Tadeo
Strengths
- Spelled the way it sounds in both Spanish and English — no silent letters, no h to explain, unlike the English Thaddeus.
- Has a ready-made short form in Teo, which works on its own and travels easily between languages.
- A documented line back to Greek and Latin, and living forms in Italian, Polish, Czech and French.
To consider
- It is climbing quickly. A child born now may find the name noticeably more common among younger kids by the time they finish school than it is among their older cousins.
- Outside Texas, California and Illinois, expect to spell it out and to hear TAD-ee-oh occasionally before people settle into tah-DEH-oh.
- Neighboring spellings exist — Thadeo, Taddeo, Thaddeus — so forms and rosters will sometimes come back altered.
Documented properties of each name — how it spells, travels and shortens — not opinions about the child.
How each is likely to age
Isaias
40%chance Isaias feels dated by 2040
Isaias sits in the calm middle of the cycle — neither chasing a wave nor sliding off one. Middle-of-the-cycle names age slowly and predictably.
Tadeo
55%chance Tadeo feels dated by 2040
Tadeo is climbing fast right now. Steep climbs tend to come with steep descents — the quicker a name arrives, the more firmly it belongs to its moment.
A reading of where each name sits on the long naming cycle — computed, not measured, and explained on the data page.
With your last name
Say both in full. The notes are facts about letters and sound — a rhyme, a shared initial, the monogram — not a verdict on either name.
Type a last name to hear Isaias and Tadeo in full.
Weighing the whole shortlist? Run the full comparison — up to eight names with your last name, initials, classroom projections and a printable report.
Decide together
Nobody names a baby alone
Still torn between Isaias and Tadeo?
Put both to the vote.
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More head-to-heads
Same measures, different pair. Sixty more are dealt daily in the arena.
Lists these names appear on
Where Isaias and Tadeo each sit in the library — alternatives in the same style, ranked by the same records.
Isaias or Tadeo — the short answers
- Which is more popular, Isaias or Tadeo?
- Isaias, in 2025: Isaias ranked #426 with 755 babies; Tadeo ranked #427 with 753 babies.
- Which name is rising faster, Isaias or Tadeo?
- Tadeo. Over the last five years Isaias moved up 46 places; Tadeo moved up 275 places.
- Which is the older name, Isaias or Tadeo?
- Isaias entered the US charts in 1915; Tadeo entered the US charts in 1968. On the American record, Isaias is the older name.
- How many people are named Isaias and Tadeo?
- About 18,000 people named Isaias are estimated to be alive in the US today. About 5,800 people named Tadeo are estimated to be alive in the US today.
- Will there be other Isaiass or Tadeos in the classroom?
- Isaias will almost certainly be the only one in school. Tadeo will almost certainly be the only one in school.
US figures from the Social Security Administration, 1880–2025. Votes are battle voters on this site, not the birth record. Data & methodology
Keep playing
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