Web App Development
Fintech Web App Development Built for Security and Scale
We build fintech web apps with bank-grade security, real-time transaction processing, and compliance-conscious architecture — shipped in weeks, not quarters.
Why Fintech Web App Development Demands a Different Approach
Fintech web app development means building with security, compliance, and audit trails as first-class engineering concerns — not bolted on in a compliance sprint six months after launch. PCI DSS requirements, KYC and AML workflows, transaction ledgers, reconciliation systems — these are not afterthought features. They are the reason your fintech product exists, and they need to be designed correctly the first time. We have built fintech apps from personal finance dashboards to investment platforms and we know which decisions cannot be undone.
Real-time financial data creates performance demands that most web app architectures cannot handle gracefully. When a user submits a wire transfer, they expect an immediate confirmation — not a loading spinner that leaves them wondering whether it went through. When account balances update, they expect instant accuracy. We build fintech web apps using PostgreSQL with optimized indexing for financial queries, Supabase real-time subscriptions for live balance updates, and idempotent API design that handles duplicate transaction submissions gracefully without double-charging.
Regulatory reporting is the feature no one wants to build and everyone needs. Whether it is SOC 2 readiness, GDPR data export endpoints, suspicious activity reporting, or tax form generation, compliance reporting must be designed into the data model early — not retrofitted after your legal team reads the audit findings. We have built fintech apps with immutable transaction records, append-only audit log tables, and export functionality that passes enterprise compliance reviews without a bespoke compliance engineering sprint.
Our Approach to Fintech web app development
Every project follows our 4-step vibe-coding process — AI handles the boilerplate, senior engineers handle the craft. From idea to live product in 3–7 days for MVPs.
Discovery
We map every financial data type your product handles, who can see it, and what regulatory requirements apply. We identify which financial workflows are core to your product versus adjacent features that can be phase two. We ask about your compliance timeline — SOC 2, PCI DSS, GDPR — and design the data model to support those requirements from the initial build.
Design
Financial UI design requires clarity over creativity. Users making financial decisions need accurate data, obvious actions, and confident confirmation states. We design fintech dashboards that surface the right numbers at the right time, with transaction flows that eliminate ambiguity at every step and error states that explain what happened and what to do next.
Build
PostgreSQL with financial-grade constraints: decimal types for monetary values instead of floating point, CHECK constraints for business rule enforcement, and triggers for audit log population. Supabase Row Level Security for account-level data isolation. Stripe for payment processing with idempotency keys on every charge. TypeScript throughout for type-safe money arithmetic.
Launch
Pre-launch financial logic review: every transaction flow tested with boundary cases, reconciliation logic verified against manual calculations, and webhook handlers stress-tested for duplicate event delivery. We run a full end-to-end payment cycle in Stripe test mode before processing a single real dollar. Post-launch monitoring alerts on transaction error rates.
What You Get
Every fintech web app development engagement includes these deliverables — scoped before we start, delivered before we invoice.
- Financial data model with decimal precision, immutable transaction ledger, and audit log tables
- Real-time account balance and transaction feed via Supabase subscriptions
- Stripe payment integration with idempotency keys and webhook handlers for full payment lifecycle
- KYC verification workflow with document upload, status tracking, and third-party provider integration
- Role-based access control for user account data, admin, and compliance officer views
- Reconciliation dashboard for transaction matching, discrepancy flagging, and export
- Regulatory reporting: GDPR data export, transaction history download, and activity summary
- Fraud detection hooks: velocity checks, anomalous amount flagging, and manual review queue
- Admin panel for account management, transaction overrides, and compliance case management
- Vercel deployment with environment isolation and structured logging for audit purposes
Tech Stack We Use
Fintech web app development at Greta uses PostgreSQL as the financial data foundation — because relational integrity, transactional writes, and decimal precision matter more than document flexibility when real money is involved. We use Supabase to manage PostgreSQL with Row Level Security for account isolation, real-time subscriptions for live balance feeds, and Supabase Vault for encrypting sensitive financial fields. Stripe handles PCI DSS-compliant payment processing, eliminating the cost and complexity of self-managed card vaulting. Next.js 15 with TypeScript provides type-safe API routes and server-rendered dashboards that load fast even with complex financial data. Every money calculation in our fintech codebase uses integer arithmetic in cents — never floating-point approximations.
Case Study
FinTrack — Real-Time Financial Dashboard
FinTrack is a personal finance aggregation platform that pulls transaction data from connected bank accounts and presents it in a real-time, categorized dashboard. We built it in 9 days: Supabase PostgreSQL with a double-entry-inspired transaction model, real-time subscriptions that push balance updates to the UI without polling, custom categorization rules stored per user, and Stripe Billing for platform subscription revenue. The toughest engineering challenge was maintaining ledger consistency when third-party data imports arrived out of order — we solved it with an idempotent import pipeline that deduplicates on external transaction IDs. FinTrack processed its first $2M in tracked transactions within 45 days of launch.
Read full case studyPricing Transparency
Fintech web app development starts at $8,000 — higher than our standard floor due to the additional security review, compliance documentation, and financial data architecture required. Full-featured fintech platforms with KYC workflows, reconciliation systems, and regulatory reporting run $25,000–$75,000 depending on regulatory scope and third-party integrations. All fintech projects include a data architecture review for financial correctness, structured logging documentation, and full code ownership. No shortcuts on security regardless of budget.
MVP
From $5,000
3–7 business days
Full Build
From $15,000
2–4 weeks
All projects include full code ownership, two revision rounds, Vercel deployment, and one week of post-launch support. No hidden fees.
Frequently Asked Questions
How do you handle money arithmetic to avoid floating-point errors?
We store all monetary values as integers in the smallest currency unit — cents for USD, pence for GBP. We never use JavaScript floats for money calculations. Calculations happen in PostgreSQL using DECIMAL types with fixed precision. Display formatting is the only place we convert to decimal representation, and only for rendering.
Can you integrate with banking APIs like Plaid or Stripe?
Yes. We integrate with Plaid for bank account connectivity and transaction data, Stripe for payment processing and platform revenue, and other financial data providers via their REST APIs. API agreements and usage costs are separate from our development fee — we help you navigate the provider selection but you pay API costs directly.
How do you prevent duplicate charges in payment processing?
Every Stripe charge we make includes an idempotency key derived from the transaction ID. If the same charge is submitted twice — due to a network error, client retry, or race condition — Stripe returns the original charge result instead of creating a duplicate. Our webhook handlers are also idempotent: processing the same event twice produces the same database state.
Can you build a multi-currency fintech product?
Yes. Multi-currency requires storing amounts with their currency code, using Stripe's multi-currency support for payment processing, and carefully designing exchange rate handling for cross-currency reporting. We have built multi-currency platforms and know which edge cases — rounding, reporting, tax — need explicit design attention.
How long does fintech web app development take?
A basic fintech product — transaction tracking, account management, Stripe integration — takes 2–3 weeks. Systems with KYC workflows, reconciliation, multi-currency support, and regulatory reporting take 4–10 weeks. We always scope precisely before starting, so you know the timeline before signing.
What compliance standards do you support?
We design fintech web apps to support PCI DSS (via Stripe for payment processing), SOC 2 (via audit logging, access control, and encryption documentation), and GDPR (via data export endpoints and deletion workflows). We do not certify compliance — that requires an independent auditor — but we build the technical controls that make certification achievable.
Do you handle regulatory reporting like AML or SAR filing?
We can build the data infrastructure that supports AML monitoring and SAR filing: transaction velocity checks, suspicious amount thresholds, flagging queues for compliance officer review, and structured data export in formats compatible with financial regulators. The actual AML program and SAR submission are compliance functions that your team manages.
Can your fintech web app scale to high transaction volumes?
PostgreSQL with proper indexing handles millions of transactions without performance degradation. The critical indexes for financial queries are on account ID, timestamp, and status columns. We configure these from day one and review the query plan for all critical transaction paths before launch. We have built fintech apps processing 50,000+ transactions per day on this architecture.
Ready to ship?
Ready to build your fintech web app?
Start Your ProjectOr reach us directly at hello@greta.agency
Written by the Greta Agency team · Last updated April 2025