What they are really asking
This one is practical and usually a good sign. The employer is planning: when the team gets help, when training can start, whether your date fits a project. They want a realistic date, not the fastest one you can imagine.
Your notice period is the time your current contract says you must work after you resign. It might be two weeks, a month or three months, depending on the job and the country. Respect it. Offering to leave your current employer without notice might sound keen, but the interviewer will wonder if you'd do the same to them one day. It's fine to mention a short break between jobs, too, if you've planned one.
A shape that works
Your notice, a date, and some flexibility. Say what notice you need to give and what that means as a date. If you can be flexible, say how, like finishing a handover early or doing some reading before you start. If there's a fixed commitment, like a booked trip, mention it now rather than later. End with a line that shows you're keen to begin.
Model answers
Listen to how each answer is built, then make it yours.
Check yourself
Practice · 3 min
Find out your real notice period, or pick a realistic one. Record a thirty-second answer that states the notice, turns it into an actual date, offers one kind of flexibility, and ends with a keen line. Listen back and check that you gave a date, not only "soon."
Your recording stays on this device. Nothing is uploaded.
Say it today
Use it once in a real conversation before tomorrow. Out loud counts, even to yourself.