1、You have my word.用在和別人討論後的追加確認。較口語化。
2、Promise 用法較為正式，莊重。
1）承諾；保證；答應 If you promise that you will do something, you say to someone that you will definitely do it.
The post office has promised to resume first class mail delivery to the area on Friday.郵局承諾於星期五恢復對這個地區第壹類郵件的遞送。
He had promised that the rich and privileged would no longer get preferential treatment.他已經保證富人和特權階層不會再得到優惠待遇。
2）答應給予；承諾給予；保證讓…得到 If you promise someone something, you tell them that you will definitely give it to them or make sure that they have it.
In 1920 the great powers promised them an independent state.1920年，列強承諾讓他們成為壹個獨立的國家。
The officers promise a return to multiparty rule.這些官員承諾恢復多黨統治。