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Calamos Investments Software Engineer Interview Guide

Calamos Investments Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

At Calamos Investments, a Software Engineer plays a critical role in bridging the gap between sophisticated financial strategies and robust, high-performance technology. As an active asset management firm, Calamos Investments relies heavily on proprietary tools, portfolio management systems, and real-time data integration to deliver value to its clients. The software engineering team is responsible for designing, building, and maintaining the systems that power investment decisions, risk management, and client reporting. This role is highly collaborative and carries significant strategic influence. You will not just write code; you will build systems that handle massive financial datasets, require high transactional integrity, and demand near-zero latency.

This guide is scoped to a Software Engineer candidate at Calamos Investments.

Focus areas

  • Programming fundamentals (coding)
  • SQL
  • Object-Oriented Programming (OOP)

The Calamos Investments interview process

Calamos Investments candidates report 3 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Phone Screen

Initial conversation with a corporate recruiter focusing on background, career goals, and role alignment.

What to demonstrate

  • Initial conversation with a corporate recruiter focusing on background, career goals, and role alignment
  • Depth in Programming fundamentals (coding)

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Panel Interview

Interview with engineering managers and senior developers to assess technical skills and conduct live coding or SQL assessments.

What to demonstrate

  • Interview with engineering managers and senior developers to assess technical skills and conduct live coding or SQL assessments
  • Depth in Programming fundamentals (coding)

How to prepare

  • Answer aloud and timed: How do you handle exception management in an enterprise-level application to ensure system stability?
  • Answer aloud and timed: Describe the concept of dependency injection and explain how it improves the testability of your code.

Final Panel Interview

Intensive onsite or virtual panel interview with cross-functional team members and senior leadership to evaluate technical capabilities and cultural fit.

What to demonstrate

  • Intensive onsite or virtual panel interview with cross-functional team members and senior leadership to evaluate technical capabilities and cultural fit
  • Depth in Programming fundamentals (coding)

How to prepare

  • Answer aloud and timed: Write a SQL query to find the second-highest salary or transaction value from a database table.
  • Answer aloud and timed: Explain the differences between an inner join, left join, and outer join, and describe a scenario where a left join is necessary.

Where candidates lose points

Master the basics

Do not spend all your time studying advanced, niche algorithms. Instead, ensure you have a flawless understanding of core OOP principles, basic data structures, and standard SQL operations.

Communicate your thought process

During coding and SQL exercises, talk through your logic out loud. Explain why you are choosing a specific approach, discuss any trade-offs, and outline how you plan to structure your code before you start typing.

Abandoning working code to chase the optimal solution

Get the straightforward version correct, state its complexity, and only then optimise, keeping the working version until the faster one passes the same cases. A correct quadratic solution with a stated path to linear beats a half-written optimal one that never ran.

Questions & practice

Implement a basic algorithm to reverse a string or array in place without utilizing built-in helper functions.

Medium · Practical Coding & Problem Solving

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Write a function to identify duplicate values within a collection and optimize it for time complexity.

Medium · Practical Coding & Problem Solving

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Walk through a live coding exercise where you must parse a structured data file and extract specific metrics.

Medium · Practical Coding & Problem Solving

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Write a SQL query to find the second-highest salary or transaction value from a database table.

Medium · SQL & Database Management

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Explain the differences between an inner join, left join, and outer join, and describe a scenario where a left

Medium · SQL & Database Management

Explain the differences between an inner join, left join, and outer join, and describe a scenario where a left join is necessary.

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

What are database indexes, how do they improve query performance, and what are the trade-offs of over-indexing

Medium · SQL & Database Management

What are database indexes, how do they improve query performance, and what are the trade-offs of over-indexing?

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

How do you ensure transactional integrity (ACID properties) when designing database schemas for financial tran

Medium · SQL & Database Management

How do you ensure transactional integrity (ACID properties) when designing database schemas for financial transactions?

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Explain the four pillars of object-oriented programming and provide a practical example of how you have used i

Medium · Object-Oriented Programming (OOP) & Core

Explain the four pillars of object-oriented programming and provide a practical example of how you have used inheritance versus composition.

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

What is the difference between an abstract class and an interface, and when would you choose one over the othe

Medium · Object-Oriented Programming (OOP) & Core

What is the difference between an abstract class and an interface, and when would you choose one over the other?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Describe the concept of dependency injection and explain how it improves the testability of your code.

Medium · Object-Oriented Programming (OOP) & Core

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

One customer endpoint stalls deliveries to every other destination

Medium · bulkhead · timeouts · saturation

The egress service delivers about 1.5k webhooks/second across 40,000 destinations, with a per-destination concurrency cap of 4 and a 10-second connect-plus-read timeout. Throughput falls to 300/second, queue depth climbs, and p99 delivery latency for unaffected destinations goes from 200 ms to minutes, while the error rate barely moves. One tenant holds 900 destination rows whose URLs share a hostname that now answers in 9.5 seconds. Explain the mechanism with the arithmetic, then give the containment in the order you would apply it.

Approach

  1. Look at saturation before errors. A flat error rate with collapsing throughput says nothing is failing, things are waiting, so the first signal to pull is in-flight request count or pool wait time rather than the error counter. This is the distinction that decides the whole investigation.
  2. Group in-flight work by resolved host, not by destination id. The cap is keyed per destination row, so 900 rows sharing one hostname buy 3,600 concurrent slots against a single host, each held for 9.5 seconds. The bulkhead was never a bulkhead for that host, and grouping by the wrong dimension is why the dashboard looked healthy.
  3. Do the arithmetic in both directions. Required concurrency is arrival rate times latency, so 1.5k/second at 200 ms needs about 300 in flight, which is entirely consumed by 3,600 slow slots; conversely whatever concurrency is left sustains rate equals concurrency divided by 9.5 seconds, which is the 300/second you are seeing. Matching both numbers is what promotes this from a plausible story to the mechanism.
  4. Explain why the circuit breaker never helped. It opens on consecutive failures, and a 9.5-second response inside a 10-second timeout is a success. Slow is not failing, so an error-rate breaker cannot see this; you need a slow-call ratio, a deadline propagated from the caller's remaining budget, or a concurrency limiter.

Follow-up

  • The host recovers to 80 ms. How long does the queue take to drain, and what does the drain do to the recovered host?
  • Where should the 10-second timeout number actually come from?

Suggested practice checklist

Built from the rounds and topics Calamos Investments candidates report.

Day 1 — Map the Calamos Investments loop

  • Write out the reported sequence: Phone Screen, Technical Panel Interview, Final Panel Interview.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.

Day 2 — Work Programming fundamentals (coding)

  • Spend the session on Programming fundamentals (coding), which Calamos Investments candidates report being tested on.
  • Write one worked example in Programming fundamentals (coding) and time yourself on it.

Deliverable: One timed worked example in Programming fundamentals (coding).

Day 3 — Work SQL

  • Spend the session on SQL, which Calamos Investments candidates report being tested on.
  • Write one worked example in SQL and time yourself on it.

Deliverable: One timed worked example in SQL.

Day 4 — Work Object-Oriented Programming (OOP)

  • Spend the session on Object-Oriented Programming (OOP), which Calamos Investments candidates report being tested on.
  • Write one worked example in Object-Oriented Programming (OOP) and time yourself on it.

Deliverable: One timed worked example in Object-Oriented Programming (OOP).

Day 5 — Answer out loud: Object-Oriented Programming (OOP) & Core Concepts

  • Answer aloud, timed: Explain the four pillars of object-oriented programming and provide a practical example of how you have used inheritance versus composition.
  • Answer aloud, timed: What is the difference between an abstract class and an interface, and when would you choose one over the other?

Deliverable: Spoken answers to 2 reported Object-Oriented Programming (OOP) & Core Concepts question(s), under time.

Day 6 — Answer out loud: SQL & Database Management

  • Answer aloud, timed: Write a SQL query to find the second-highest salary or transaction value from a database table.
  • Answer aloud, timed: Explain the differences between an inner join, left join, and outer join, and describe a scenario where a left join is necessary.

Deliverable: Spoken answers to 2 reported SQL & Database Management question(s), under time.

Day 7 — Answer out loud: Practical Coding & Problem Solving

  • Answer aloud, timed: Implement a basic algorithm to reverse a string or array in place without utilizing built-in helper functions.
  • Answer aloud, timed: Write a function to identify duplicate values within a collection and optimize it for time complexity.

Deliverable: Spoken answers to 2 reported Practical Coding & Problem Solving question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

How do you handle exception management in an enterprise-level application to ensure system stability?

Medium · Object-Oriented Programming (OOP) & Core

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Walk me through your resume and highlight a project where you had to make a difficult technical trade-off.

Medium · Behavioral & Professional Experience

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe a time when you had to work with a difficult stakeholder or team member. How did you resolve the conf

Medium · Behavioral & Professional Experience

Describe a time when you had to work with a difficult stakeholder or team member. How did you resolve the conflict and complete the project?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you stay updated with emerging technologies, and how have you applied a newly learned skill to your pro

Medium · Behavioral & Professional Experience

How do you stay updated with emerging technologies, and how have you applied a newly learned skill to your professional work?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?