Thank them for it, stay with your decision, and keep the relationship good. Fill in the boxes and the email writes itself.
Filled in with an example. Type in the boxes to make it yours.
Subject: Thank you for the offer
Hi Mere,
Thank you for the counter-offer, and for wanting me to stay. It means a lot.
I have thought about it carefully and I am going to keep to my decision. My last day will still be Friday 30 October 2026.
I will make the handover as smooth as I can, and I hope we stay in touch.
Kind regards,
Sam Hollis
Reply within a day or two, and do not reopen the reasons you are leaving. A counter-offer usually fixes the pay, not the reasons you started looking.
If you are genuinely tempted, read the article below before you answer.
More on this: Counter offers: should you stay when your employer matches the new job's pay?
Keep every letter with the job it belongs to: jobtracker.co.nz is free while you're between jobs. See all the letter templates.