How do you manage underperforming employees?

In this article

1. Before you start
2. Why interviewers ask this
3. Managing underperforming employees from first principles
4. The Staff-level answer
5. The rubric
6. Three variants of this question
7. Common mistakes
8. Follow-up questions
9. Sources

Before you start

This page is one answer in the engineering manager interview questions guide; the people management round explains where the question appears.

Why interviewers ask this

A manager who handles underperformance badly pays twice: the struggling engineer never gets a real chance to improve, and the rest of the team carries the load and watches what happens. Candidates report this question, in many wordings, in engineering manager loops at AI labs and large tech companies. Interviewers use it to see whether you diagnose before you judge, whether you stay fair and keep records, and whether you act instead of hoping.

A weak answer jumps straight to a plan or to firing. A strong answer names a sequence: diagnose, talk, support, review, decide. A Staff-level answer adds the manager's own share of the cause and the cost of waiting too long, and it is grounded in one real, anonymised case. This page covers the general method; how to handle a low performer is the single-case version.

Managing underperforming employees from first principles

Performance gap

A performance gap is the measurable difference between the work a person delivers and the standard the role requires, stated in observable results and behaviors rather than impressions, so that both the manager and the employee can check it.

Cause diagnosis

Cause diagnosis is the step in which a manager tests why a performance gap exists, by checking unclear expectations, missing skill, low motivation, poor context and personal circumstances, before choosing a response that fits that cause.

In plain words

Think of a doctor. A good doctor asks questions and runs tests before prescribing, because the same symptom, such as tiredness, has many causes and each needs a different treatment. Managing underperformance works the same way. The analogy breaks in one place: a doctor owes the patient only care, while a manager also owes the team fair results. That is why the plan needs a deadline.

In one precise sentence, you measure the performance gap, find its cause, agree support with a deadline, and decide from the evidence at the review dates.

The reason for this order is that each step depends on the one before it. Without a measured gap, a cause is only a guess. Without a cause, support is random. Without a deadline and records, the final decision rests on memory and mood rather than on evidence both sides can check.

Step 1: Diagnose the cause before you judge the person

Cause diagnosis starts with the manager's own part: were the expectations clear, specific and written down? Then work through a checklist: skill (can they do it yet?), motivation (do they want to?), context (workload, tools, a broken team process) and circumstances (health, family). This is a working checklist from management practice, not a published standard. Acas notes that a situation can look like a conduct issue yet turn out to be capability, so involve HR early if health may be a factor. Input: the gap and your evidence. Output: a stated cause, even if provisional. You now know which response fits: clarity needs a conversation, skill needs coaching, context needs you to fix the system.

Step 2: Talk privately and agree support and a deadline

The conversation is private and two-way. The Acas guide says minor performance cases are usually best dealt with informally. Describe specific work and its impact, ask for the person's view, then agree three things: what good looks like, what help you will provide, and when you will review. Keep a written note and share it with the employee, so both sides remember the same agreement. The Acas guide advises keeping written records of formal cases, and Acas suggests sharing a written record of an improvement plan with the employee. Input: the diagnosis. Output: an agreed, written set of outcomes, support and a deadline. You now have something both sides can measure, and a record to return to at each review.

Step 3: Review on the agreed dates and decide from evidence

At each review you compare results with the agreed outcomes and decide. If the gap closed, stop and say so. If the cause was yours, such as unclear goals, fix it and reset. If support worked partly, adjust and set a nearer date. If the gap persists despite clear expectations and real support, move to a formal route with HR.

A performance improvement plan (PIP) is a written plan that sets out the gap, the required outcomes, the support offered and the review dates. Acas describes what an improvement plan can contain. A UK employment-law explainer describes a move from informal action to formal capability steps, with a genuine chance to improve before dismissal. Rules differ by country, so follow your HR team and local law.

1 · Diagnose2 · Talk and agree3 · Review and decideReplay

Step-by-step description

1. Find the cause before judging.
2. Agree support and a deadline.
3. Decide from evidence.

• Diagnose the cause before you judge the person.
• Talk privately and agree support and a deadline.
• Review and decide from evidence on the agreed dates.

Example: what the numbers can look like

The case below is illustrative: an invented engineer, invented task counts and a plan length chosen for illustration, not a measurement. In weeks one to four the engineer finishes 7 of 19 committed tasks, a completion rate of 36.8 percent.¹ Diagnosis finds that the goals were vague. The manager and engineer then agree a target of 80 percent, weekly pairing sessions and review dates.¹

In weeks five to eight the rate is 70.0 percent, still 10.0 points under target.¹ In weeks nine to twelve it is 85.0 percent, above target.¹ A 60-day plan with check-ins every 14 days has four check-ins, which is also illustrative.¹ The point is the method: the manager measures against a stated target at fixed dates instead of relying on impressions.

Text description of the diagram

• The illustrative completion rate is 36.8 percent in weeks one to four.
• It is 70.0 percent in weeks five to eight and 85.0 percent in weeks nine to twelve.
• The agreed target is 80 percent.

The Staff-level answer

Then anchor it in one real, anonymised case: the cause you found, what you changed and the result.

What makes it Staff-level: it diagnoses before judging, admits the manager's share, says what evidence drives each decision and names the cost of delay. Say it in that order: diagnosis, conversation, plan, review, decision, trade-off.

The rubric

Treat the table as advice about what a strong answer shows, not as how any named company scores interviews.

Three variants of this question

What if the underperformer is a senior engineer?

The method stays the same, but the diagnosis shifts toward scope, ambiguity and influence rather than basic skill. Name the expectation at their level, such as the quality of decisions or how they raise others, and give feedback with the same evidence you would give anyone.

What if the cause is a personal problem?

Listen first, involve HR early and separate support from the performance conversation. Adjust workload or timing where you can, and keep the written outcomes realistic, because a plan built for someone in crisis fails for reasons no coaching fixes.

How do you manage underperforming employees you inherited?

Check the history before judging: what was agreed, what was documented and what support existed. Reset expectations in your first weeks, then treat any gap as new evidence you collect yourself. The page on inheriting a team covers the first 90 days, and managing the performance of your team covers the wider picture.

Common mistakes

• "I'd put them on a plan right away." (wrong) It skips diagnosis and the informal step that guidance recommends. (right) "I'd first check expectations and cause, then talk, then decide whether a formal plan is needed."
• "It is a motivation problem." (wrong) That is an assumption, and skill, clarity and context can cause gaps too. (right) "I'd test each cause before choosing a response."
• "I'd tell them the team is watching." (wrong) It shames the person and adds no information. (right) "I'd describe the work and its impact on the team's goals."
• "I'd keep it verbal." (wrong) Without notes, nobody can show what was agreed. (right) "I'd record each conversation and share the note with the employee."
• "I'd wait for the review cycle." (wrong) Waiting lets the team absorb the cost. (right) "I'd raise it as soon as I see the pattern."

Follow-up questions

How do you manage underperforming employees without a formal plan?

Use regular one-on-ones, specific feedback and coaching, with written notes of what you agreed. The Acas guide says minor performance cases are usually best dealt with informally, and the one-on-ones page covers how to run the meeting.

When do you start a performance improvement plan?

Start one when informal steps have been tried, expectations were clear and support was real, yet the gap remains. Involve HR first, because the plan's wording and process matter if it later leads to a dismissal.

What do you write down, and why?

Record the expectations, the conversations, the support offered, the review dates and the evidence compared at each one. A UK guide says such records show fairness later, and they also keep you honest about what you actually agreed.

How do you tell a skill problem from a motivation problem?

Ask whether the person can do the task when it is clear and supported. If results improve with coaching, it was skill or clarity; if they stay low while you have removed the obstacles, motivation or fit is the likelier cause. The growing engineers page covers the coaching side.

What if the engineer reaches only 70 percent at the first review?

Compare it with the baseline: in the illustrative case above, 70.0 percent is a large rise from 36.8 percent but still 10.0 points under target.¹ Acknowledge the progress, keep the support and set a nearer date. Also ask how the rest of the team is coping, as the team health page explains, and connect the answer to your management philosophy.

Have you ever had to let someone go?

Answer with one real, anonymised case: the cause, the support, the review evidence and the outcome. Acas describes outcomes of a failed plan such as an extension to the timeline, or a final written warning followed by dismissal if the issue continues. A role change is another route to discuss with HR.

Sources

1. Problems with an employee's performance - Performance management — Acas (page read 2026-10-26; publication date not shown), 26 Oct 2026
2. Discipline and grievances at work: the Acas guide — Acas, 1 Jul 2020
3. Managing Poor Performance at Work 2026 (UK Guide) — Davidson Morris (page read 2026-10-26), 26 Oct 2026