When you need to make a promise in English, you can use these common phrases and expressions:
Making promises:
a. I promise that I will finish the job on time.
b. I promise you that that’s the truth.
c. I swear I will never leave you.
d. I swear I won’t let you down.
e. I assure you that I will return the book tomorrow morning.
f. I assure you that I will be there on time.
g. Believe me, I won’t make you disappointed.
h. Trust me, I can do it.
Useful Responses:
a. Thank you.
b. I believe you.
c. All right. Keep your promise.
d. I hope you will keep your words.
e. Just let the time answer it.
“As soon as one promises not to do something, it becomes the one thing above all others that one most wishes to do”
Georgette Heyer
Learning English is Fun! 