•SYSTEM DESIGN
Capital One System Design Questions
Every system design problem candidates reported at Capital One between September 2025 and September 2026, most-asked first. Each one links to a full solution.
Problems
7
Candidate reports
8
Asked more than once
1
start here
Question type
7 HLD
Topics Capital One tests
Design a geography-aware virtual card service
Design a virtual credit card service for a bank: customers generate virtual card numbers (single-use, merchant-locked, or with spending limits, possibly geography-aware) linked to their real account. On each transaction the…
Also worded as: Validate virtual credit card transactions from encoded IDs
Design Credit-Card Authorization, Limit Decisions, and Reporting
Design a credit card system that supports application login, real-time payment authorization with fraud detection, credit-limit decisions (approve or deny based on available credit), a view of the user's spending, and monthly…
Design a credit card portal
Design a credit card customer portal: users log in, view card details, balance, available credit and statements, see transactions, make payments, set alerts, and manage their card (lock/unlock, replace). Discuss authentication…
Design a mobile banking app backend
Design a secure, highly available backend for a mobile banking app: accounts and balances, transaction history, transfers and bill payments, notifications, and customer profile. Discuss API and service design, the data model…
Design a highly reliable account balance system
Design a highly reliable backend service that stores and updates user account balances (a wallet or bank ledger). Support deposit, withdraw, transfer between accounts, and balance/history queries. Requirements: balances are never…
Design a cross-region event processing platform
Design a cross-region event processing platform: producers in multiple regions send events continuously; the platform stores them durably and delivers them to multiple consumer groups for processing. Requirements: no data loss if…
Threaded replies in a chat app (Slack/Teams)
Design a real-time chat system like WhatsApp or Slack supporting one-to-one and group conversations (and, for Slack variants, workspaces, channels and threaded replies). Users send and receive messages with low latency, see…
Duplicate reports of the same problem are merged and counted.
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What system design questions does Capital One ask?
Candidates reported 7 distinct system design problems at Capital One between September 2025 and September 2026, including Design a geography-aware virtual card service, Design Credit-Card Authorization, Limit Decisions, and Reporting, Design a credit card portal.
How to prepare for Capital One system design interview?
Start with the Capital One problems reported most often, work through each full solution, then practice explaining a design end to end under time pressure in a mock interview.
What is the difference between HLD and LLD at Capital One?
HLD (High-Level Design) focuses on system architecture, scalability, and component interactions. LLD (Low-Level Design) dives into class diagrams, API contracts, and database schemas. Capital One tests both.