고맙다 vs 감사하다: Two Words for 'Thank You'

Just as Korean splits "sorry" into 미안하다 and 죄송하다, it splits "thank you" into two roots — 고맙다 and 감사하다 — and the logic is exactly parallel. Both mean "be thankful," both take fully polite endings, and the choice between them is about register and warmth, not about how grateful you are. 감사하다 is the formal, public, service-counter word; 고맙다 is the warm, personal, heartfelt one. Neither is "more polite" in the sense of "more correct" — 고마워요 to a friend is not a downgrade from 감사합니다, it is the right register. Getting this split right is the difference between sounding like a stiff announcement and sounding like a real person. There is also a conjugation trap hiding inside 고맙다 that snares nearly every beginner, and we'll defuse it.

The two roots

고맙다 is native Korean. It is warmer and more personal, the thanks you give to friends, family, and anyone you feel real gratitude toward. Its polite forms are 고마워요 (해요체) and 고맙습니다 (formal), and its 반말 is 고마워.

감사하다 is Sino-Korean (from 感謝). It is the default public, formal, service register — what you say to clerks, strangers, in announcements, in speeches. Its forms are 감사해요 and, most commonly, 감사합니다.

The word 덕분에 ("thanks to [you/it]") is the natural partner of heartfelt thanks — it credits the other person for a good outcome and pairs far more often with 고맙다 than with cool, formal 감사하다.

Both are polite — pick by the moment

Because 감사합니다 is the first "thank you" most learners memorize, many treat it as the only correct thanks and deploy it everywhere, including with close friends — where it lands as oddly cold and distant, like thanking your best friend with a business email. The fix is to match the word to the relationship:

The conjugation trap: 고맙다 is a ㅂ-irregular

Here is where 고맙다 ambushes learners. Its stem ends in ㅂ (고맙-), and ㅂ-final descriptive verbs are irregular: before a vowel ending, the ㅂ turns into 우, which then fuses with the following 어 to give 워. So 고맙 + 어요 does not yield ×고맙어요 — it yields 고마워요. The 반말 is 고마워, and the past is 고마웠어요.

The reason the ㅂ stays put in 고맙습니다 but transforms in 고마워요 is simple: the ㅂ-irregular only fires before a vowel. 습니다 begins with a consonant, so the ㅂ survives; -어요 begins with a vowel, so the ㅂ becomes 우. (감사하다, being a regular 하다 verb, has no such drama: 감사해요, 감사합니다.) For the full pattern and the other ㅂ-irregular verbs it shares it with (덥다 → 더워요, 쉽다 → 쉬워요), see the ㅂ-irregular.

Why English speakers get this wrong

English has one "thank you" and stretches it by tone, so learners look for the one "most correct" Korean equivalent — and settle on 감사합니다 because it sounds formal and safe. But Korean chose the word for you the moment you knew who you were thanking and how formal the setting was. Reserve 감사합니다 for the public and formal, and let 고마워(요) do the warm, personal work it exists for. And whenever you use 고맙다, remember it is a ㅂ-irregular: the surface form is 고마워요, never the tempting-but-wrong ×고맙어요.

This is the exact same architecture as the apology split (see 죄송 vs 미안): a Sino-Korean root for the formal/public register (감사, 죄송) and a native root for the warm/personal one (고맙, 미안), with the choice driven by relationship, not intensity.

Common Mistakes

1. ×고맙어요 — mis-conjugating the ㅂ-irregular. The ㅂ becomes 우 before a vowel, giving 고마워요.

2. Thanking a close friend with 감사합니다. It creates cold distance; use warm 고마워.

3. Assuming 감사합니다 is the only 'real' thank-you. 고마워요 is fully polite and often the better fit.

4. Wrong past form ×고맙았어요. Past follows the same ㅂ → 우 change: 고마웠어요.

Key Takeaways

• 고맙다 (native) = warm, personal thanks (고마워 / 고마워요 / 고맙습니다). 감사하다 (Sino-Korean) = formal, public, service thanks (감사해요 / 감사합니다). Both are fully polite.
• The split is register + warmth, not degree of gratitude — exactly parallel to 죄송 vs 미안.
• Don't default to 감사합니다 everywhere; with friends it reads as cold. Warmth is the politeness there, and warmth is 고마워.
• 고맙다 is a ㅂ-irregular: the ㅂ becomes 우 before a vowel → 고마워요 (never ×고맙어요), past 고마웠어요 (never ×고맙았어요). The ㅂ only survives before a consonant ending (고맙습니다).
• 덕분에 ("thanks to you") is the natural partner of heartfelt 고맙다.