-아/어야 되다
must, have to — spoken Korean
States an obligation. This is the form you hear in conversation. The written counterpart, -아/어야 하다, is covered on its own page.
Build it
Pick a verb
When to use it
The vowel follows the -아요/어요 rule with the usual merges: 가야 돼요, 먹어야 돼요, 해야 돼요. It works with adjectives too: 건강해야 해요.
Korean does not distinguish “must” from “have to” the way English does; one form covers both external rules and personal necessity. For the past, the tense goes on 되다: 어제 일찍 가야 했어요.
The hard part is the negative. English “must not” and “don’t have to” look like a pair, but Korean builds them from different constructions entirely: prohibition is -(으)면 안 되다, and absence of obligation is 안 -아/어도 되다. Negating this ending directly does not produce either.
How to attach it
| Stem type | Form | Example |
|---|---|---|
| Last vowel ㅏ or ㅗ | -아야 되다 | 가다 → 가야 돼요 |
| Any other vowel | -어야 되다 | 먹다 → 먹어야 돼요 |
| 하다 verbs | 해야 되다 | 공부해야 돼요 |
| Written, formal | use -아/어야 하다 | 제출해야 합니다 |
| Past | tense on 되다 | 가야 했어요 |
| Not required | 안 -아/어도 되다 | 안 가도 돼요 |
In use
내일까지 끝내야 돼요.
I have to finish it by tomorrow.
약을 먹어야 돼요.
You have to take your medicine.
조금 더 기다려야 돼요.
We have to wait a little longer.
매일 공부해야 돼요.
You have to study every day.
이번 주까지 신청해야 돼요.
You have to apply by this week.
여권을 꼭 가져와야 돼요.
You must bring your passport.
Compared with
-(으)면 안 되다
Obligation and prohibition are separate constructions, not one negated. Keeping the three-way set straight solves most modal errors at this level.
가야 돼요. (must go) / 가면 안 돼요. (must not go) / 안 가도 돼요. (need not go)
-(으)세요
-아/어야 되다 explains that something is necessary; -(으)세요 tells the person to do it. Advice often uses the first because it feels less like an order.
약을 드세요. (take the medicine) / 약을 드셔야 돼요. (you need to take it)
-는 게 좋겠다
A softer recommendation. Where -아/어야 되다 states a requirement, this suggests the better course.
병원에 가야 돼요. (you have to go) / 병원에 가는 게 좋겠어요. (you’d better go)
Watch out
주말에도 공부하어야 돼요.
주말에도 공부해야 돼요.
하다 becomes 해 before this ending, as it does throughout. 운동해야, 일해야, 전화해야.
여기에서 담배를 안 피워야 돼요.
여기에서 담배를 피우면 안 돼요.
Negating the verb inside gives an odd “you are obliged not to”. Prohibition has its own construction.
숙제를 하지 않아야 돼요? — asking whether it can be skipped
숙제를 안 해도 돼요?
Absence of obligation is 안 -아/어도 되다. This is the form to reach for whenever English says “don’t have to.”
Next
koreangrammarmap.com