How Long Should User Interviews Be? Length and Duration Best Practices

Quick answer: target durations by research type

These targets assume the interview is well-designed. A bloated 60-minute discovery interview that should have been 30 minutes still bleeds quality after minute 35 — duration alone doesn't buy depth.

Why length matters more than people think

Interview length affects three things simultaneously:

1. Completion rate — the percentage of started interviews that finish. Longer = lower.
2. Answer depth — substantive answers vs. one-word responses. Peaks in the middle of an interview, then declines.
3. Cost — researcher time, scheduling overhead, transcription, analysis, and incentive size all scale with length.

The classic mistake is treating "more time = more insight". Past a certain point, you get diminishing returns and degraded data because fatigued respondents answer faster, less specifically, and less honestly. So shorter, sharper interviews often outperform long meandering ones.

The fatigue curve

Across thousands of user interviews, answer quality follows a predictable arc:

• Minutes 0-5: Warming up. Answers are short and surface-level.
• Minutes 5-15: The sweet spot. Respondents are engaged and substantive. The richest data lives here.
• Minutes 15-30: Sustained engagement is possible but requires good moderation. Depth declines slowly.
• Minutes 30-45: Fatigue starts. Answers shorten. Stories get formulaic.
• Minutes 45+: Diminishing returns on most research goals. Only deeply emotional or technical topics sustain depth past this point.

This is why a well-designed 10-minute AI-moderated interview can match a 30-minute traditional one — you're extracting the same minutes 5-15 sweet spot, just without the surrounding overhead.

Foundational discovery: 45-60 minutes

When to use this length: opening a brand new research area, building a persona from scratch, understanding a complex workflow, or doing customer development on a problem space you've never explored.

Budget breakdown:

• Opening (5 min) — consent, warm-up, context setting
• Background story (10-15 min) — who they are, what their world looks like
• Current behavior (15-20 min) — how they solve the problem today, what they've tried
• Pain and opportunity (10-15 min) — where it breaks, what they wish was different
• Closing (5 min) — anything we missed, referrals

Going past 60 minutes adds little. If you're consistently hitting time, your guide is too broad — split it into two studies.

Evaluative / solution interviews: 20-30 minutes

When to use this length: testing a prototype, validating a positioning narrative, evaluating a feature concept, or pricing research.

The goal is targeted reaction to specific stimuli, not open-ended exploration. Most evaluative interviews collapse into 2-3 core questions surrounded by probing, so 20-30 minutes is plenty.

AI-moderated generative interviews: 8-15 minutes

This is the sweet spot for most modern customer research. Platforms like Koji can run discovery-style interviews in roughly a third of the time a human moderator needs because:

• No scheduling overhead. The respondent starts whenever it suits them — no 5-minute "let me get set up" tax at the start.
• No note-taking pauses. The AI captures everything in real time without slowing the conversation.
• Adaptive coverage. If a respondent has clearly covered a topic in their answer to Q2, the AI doesn't mechanically ask Q3 about the same thing.
• Probing only where it matters. Each question has a maxFollowUps setting (0-3). Strategic questions probe deep; routine ones move on quickly.

Result: a 10-minute Koji interview routinely yields the substantive content of a 25-30 minute human-moderated session.

Pulse and continuous AI-moderated: 5-10 minutes

For ongoing research programs — monthly NPS follow-ups, post-purchase debriefs, beta feedback loops, support-ticket deep-dives — shorter is better. Respondents will come back for a 5-minute conversation; they won't for a 30-minute one. See customer interview cadence for cadence design.

A typical 7-minute Koji pulse interview has:

• 1 contextual opener
• 2-3 core questions (mixing open-ended and structured)
• 1 strategic question with deep probing
• 1 closing prompt

That's it. Resist the urge to "while we have them, ask about X".

The opening and closing budget

Two universal rules regardless of interview length:

• Opening should be 5-10% of total time. For a 10-minute interview, that's 30-60 seconds. For a 60-minute interview, 3-6 minutes. Anything more eats into the substantive minutes.
• Closing should be 5-10% of total time. Reserve time for "is there anything you wish I'd asked" — this single question routinely surfaces the most surprising insights in a study.

The middle 80-90% is your core research time — that's where the questions in your guide get answered.

Compressing without losing depth

The mistake most teams make when trying to shorten interviews is cutting questions. The better move is to change question types and rely on AI probing.

Example: a 30-minute interview with 12 open-ended questions can compress to a 12-minute interview by:

• Converting 5 of the questions to structured types (scale, single_choice, ranking) — see the structured questions guide. These take 15-20 seconds each vs. 90-120 seconds for open-ended.
• Keeping the 4 most strategic questions as open-ended with maxFollowUps: 2 — depth where it matters.
• Dropping the 3 questions that were really "nice to know" — they belong in a separate study or a survey.

Same insight surface area, less than half the time. This is the fundamental advantage of AI-native research tools: you don't have to choose between depth and speed.

How to set expectations on the landing page

State the expected duration explicitly on the interview landing page. Always.

Good: "About 10 minutes. Choose voice or text." Bad: "A few questions about your experience."

Stating duration upfront lifts completion rates 5-15 percentage points because respondents self-select correctly. Always slightly under-promise: if your design target is 8 minutes, say "under 10".

Measuring actual interview length

In your Koji study analytics, look at:

• Median duration — your typical interview length
• P75 / P95 duration — your long tail; if these are 2-3x median, your AI probing is over-firing on a subset of respondents
• Duration vs. quality score — does longer correlate with higher quality? Often not past minute 15

If your P95 is creeping up, lower maxFollowUps on the questions that show the most variance.

Common length mistakes

• Padding with rapport. "How was your weekend?" wastes the first 90 seconds when the respondent is most alert. Skip it; the AI handles warmth conversationally.
• Asking "while I've got you" questions. Every extra question you add costs 60-120 seconds and a few points of completion.
• Treating long = thorough. A 10-minute focused interview beats a 40-minute meandering one on insights per minute.
• Not telling participants the length. Cardinal sin. Every interview landing page should state expected duration.
• Using deep probing (maxFollowUps: 3) on every question. Reserve it for the 1-2 most strategic questions.

Related Resources

• Structured Questions Guide — how question types affect interview duration
• How Many User Interviews Do You Need? — sample size vs. length tradeoffs
• Probing and Follow-Up Questions — controlling probing depth
• AI-Moderated Interviews — why AI moderation compresses time
• Semi-Structured Interview Guide — balancing structure and flexibility
• How to Conduct User Interviews — moderation fundamentals
• Customer Interview Cadence — when shorter recurring interviews beat one big one
• Remote Interview Best Practices — running interviews at distance