Side-by-side audit matrix recommending the 8% Flat Rate or Graduated Rates with exact peso delta.
home / projects / bir-copilot ← tax calculations made painless ✓
no. 01 · open source tax calculatorBIR CO-PILOT PH
An open-source Philippine tax calculator and statutory deductions platform for freelancers, self-employed professionals, and employees. Compare 8% flat vs graduated income tax, fill out BIR Form 1701A with zero guesswork, and calculate DOLE, SSS, PhilHealth, and Pag-IBIG contributions with precision.
8% vs GradTRAIN & CREATE Act audit
100% Clientzero server storage, total privacy
MIT Licensefirst open-source release
The problem
Philippine tax compliance is notorious for confusing bracket structures, complex exemptions, and opaque deductions. Freelancers and sole proprietors routinely overpay or get penalized simply because deciding between the 8% Flat Rate and Graduated Income Tax with OSD requires hours of manual arithmetic. Meanwhile, employees lack an easy way to verify statutory deductions (SSS 2025 table, PhilHealth 2024-2025, Pag-IBIG HDMF, DOLE Factor 261/313/365).
Architecture
Next.js 14 App Router + TypeScript + Tailwind CSS
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Client-Side Mathematical Engine (Decimal.js / Precise Tax Math)
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8% vs Graduated Side-by-Side Audit Matrix
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eBIRForms 1701A Field Mapper & Deduction Visualizer
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Zero Cloud Tracking & Complete Offline/Local Operation
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Client-Side Mathematical Engine (Decimal.js / Precise Tax Math)
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8% vs Graduated Side-by-Side Audit Matrix
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eBIRForms 1701A Field Mapper & Deduction Visualizer
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Zero Cloud Tracking & Complete Offline/Local Operation
What I built
- Dual-Regime Tax Comparator: Real-time side-by-side audit comparing the 8% Flat Gross Rate vs Graduated Rates with either 40% OSD or Itemized Deductions. Automatically highlights the optimal regime with exact peso savings.
- eBIRForms 1701A Field Cheat Sheet: Directly maps calculations to line-item box numbers for BIR Form 1701A, eliminating filing ambiguity.
- Statutory Deductions Engine: Complete calculators for SSS (with 2025 contribution tables & WISP), PhilHealth (2024-2025 rates), Pag-IBIG HDMF (2024 revised caps), and DOLE working-day factors (261, 313, 365 days).
- Privacy-First Client-Only Execution: All financial calculations occur exclusively inside the client's browser using `localStorage`. No income or financial data ever reaches an external server.
- Dark & Light Theming: High-contrast interface with seamless dark and light mode toggle.
Challenges solved
- Floating point accuracy: Financial calculations require strict rounding and precision; implemented precise decimal math to avoid JS floating-point inaccuracies.
- Tax reform compliance: Formulated rules respecting both TRAIN Law thresholds (₱250,000 non-taxable base) and CREATE Act graduated income brackets.
- Open source distribution: Packaged under the MIT License with a modular architecture so Filipino developers can audit, contribute, and extend the rules engine.
Visual Walkthrough
BIR Form 1701A field-by-field cheat sheet for frictionless filing into the BIR desktop app.
Statutory deductions engine with SSS 2025 tables, PhilHealth, Pag-IBIG caps, and DOLE working-day factors.
Full light mode theme support for high-contrast accessibility.
Next.js 14React 18TypeScriptTailwind CSSDecimal.jsOpen SourceMIT License
“In this world, nothing is certain except death and taxes.”
— Benjamin Franklin