Verbseoul.
하다 verb
약속하다yaksokhadato promise

To say to promise politely in the present tense, use 약속해요 (yahg-ssoh-kae-yoh). Below is the full conjugation of 약속하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
약속해
yahg-ssoh-kae
약속해요
yahg-ssoh-kae-yoh
약속합니다
yahg-ssoh-kahm-nee-dah
Past
약속했어
yahg-ssoh-kae-ssuh
약속했어요
yahg-ssoh-kae-ssuh-yoh
약속했습니다
yahg-ssoh-kae-sseum-nee-dah
Future
약속할 거야
yahg-ssoh-kahl- -guh-yah
약속할 거예요
yahg-ssoh-kahl- -guh-yae-yoh
약속할 겁니다
yahg-ssoh-kahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
약속하세요
yahg-ssoh-kah-sae-yoh
Suggestion / Let's Polite (요)
약속해요
yahg-ssoh-kae-yoh
Question Polite (요)
약속해요?
yahg-ssoh-kae-yoh-?
Connective “and” — (고)
약속하고
yahg-ssoh-kah-goh
Conditional “if” — (면)
약속하면
yahg-ssoh-kah-myuhn
Noun form — (기)
약속함
yahg-ssoh-kahm