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Financial software cannot afford to be “almost right.” A duplicated request can charge a customer twice. A rounding error can break reconciliation. An out-of-order event can expose a balance that does not exist. And an audit trail without reliable evidence can turn a technically sound system into an operational and regulatory risk.

Fundamentals of Software Engineering for Fintechs provides a practical foundation for designing financial systems that remain correct, auditable, and resilient under real-world conditions. Starting with the fundamentals of money modeling, the book progresses through double-entry ledgers, idempotency, distributed consistency, payment processing, reconciliation, security, observability, and invariant-driven testing.

You will learn how to:

Represent monetary values without silent precision or rounding errors.
Design balanced, immutable double-entry ledgers.
Prevent duplicate financial effects across APIs, queues, and background jobs.
Model authorization, capture, settlement, refunds, reversals, and disputes.
Distinguish ledger balance, available balance, and external settlement state.
Reconcile internal records with processors, banks, and payment networks.
Build audit trails that support investigations, incidents, and compliance reviews.
Test financial invariants under concurrency, retries, delays, and partial failures.
Use metrics and controls that reveal actual financial and operational risk.

Written for software engineers, architects, technical leaders, and professionals working in product, risk, finance, and operations, this book combines mental models, implementation patterns, pseudocode, SQL examples, checklists, and practical exercises.

It does not prescribe a single architecture or technology stack. Instead, it teaches you how to make financial assumptions explicit, convert business rules into enforceable invariants, preserve reliable evidence, and design systems in which every balance and transaction can be explained.

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Kick off your book project, get started with GhostAI, get better at marketing, or spend the day doing all three! Free live workshops on Zoom. Saturday, June 27, 2026.

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