I owe you one.

Meaning

Expressing gratitude with a promise of returning the favor.

Examples

• John: Thanks for covering for me at work today.
• Alice: No problem. <b>I owe you one</b>.
• John: Really? Anything you need, just let me know. I’m glad to help.
• Alice: I appreciate that. I'll keep that in mind. <b>I owe you one</b>.