Every year, thousands of mortgage brokers, accountants, and HR professionals in Canada manually re-enter data from T4 slips. Box 14, box 22, box 16, box 18 — copied one by one from a PDF into a spreadsheet or loan application.
It's slow, error-prone, and completely unnecessary in 2025.
In this article, I'll show you how to automate T4 extraction in under 10 minutes using a REST API — no OCR libraries, no ML model, no infrastructure to maintain.
What is a T4 Slip?
A T4 (Statement of Remuneration Paid) is a Canadian tax document issued by employers to employees every year. It reports employment income and all payroll deductions to the CRA.
Key boxes that matter for most workflows:
| Box | Description |
|---|---|
| Box 14 | Employment income |
| Box 16 | CPP contributions |
| Box 17 | QPP contributions (Quebec) |
| Box 18 | EI premiums |
| Box 22 | Income tax deducted |
| Box 24 | EI insurable earnings |
| Box 26 | CPP/QPP pensionable earnings |
The Problem With Traditional OCR
Most OCR libraries (Tesseract, AWS Textract, Google Document AI) are general-purpose. They extract raw text — but they don't understand that "14" followed by a number means "employment income."
You still end up writing a parser, maintaining regex patterns, and handling every variation of T4 layout across different payroll systems (ADP, Ceridian, Payworks, Nethris...).
A Better Approach: Document Intelligence API
Instead of building and maintaining OCR + parsing logic, you can call an API that handles everything — including scanned T4s.
Here's how it works:
- Convert the T4 PDF to base64
- Send it to the API
- Get back structured JSON with all boxes
Step-by-Step Implementation
Step 1 — Convert the PDF to Base64
Node.js:
const fs = require('fs');
const pdfBuffer = fs.readFileSync('./t4-2024.pdf');
const base64 = pdfBuffer.toString('base64');
Python:
import base64
with open("t4-2024.pdf", "rb") as f:
base64_str = base64.b64encode(f.read()).decode("utf-8")
PowerShell (Windows):
$base64 = [Convert]::ToBase64String([IO.File]::ReadAllBytes("C:\path\to\t4-2024.pdf"))
Step 2 — Call the API
const response = await fetch('https://docusense.stackapi.dev/api/v1/documents/t4', {
method: 'POST',
headers: {
'Authorization': 'Bearer YOUR_API_KEY',
'Content-Type': 'application/json',
},
body: JSON.stringify({
fileBase64: base64,
mimeType: 'application/pdf',
taxYear: 2024,
language: 'fr' // or 'en'
})
});
const result = await response.json();
console.log(result.data);
Step 3 — Handle the Response
{
"success": true,
"data": {
"taxYear": 2024,
"employerName": "Entreprise ABC Inc.",
"payrollAccountNumber": "123456789RP0001",
"employeeName": "Jean Tremblay",
"socialInsuranceNumber": "***-***-456",
"province": "QC",
"boxes": {
"box14": 72000.00,
"box16": null,
"box17": 3799.80,
"box18": 1049.12,
"box22": 17850.00,
"box24": 61500.00,
"box26": 68500.00,
"box44": null,
"box46": 500.00
}
}
}
Notice that the SIN is automatically masked (***-***-456) — privacy is handled for you.
Real-World Example: Mortgage Pre-Qualification
Here's a complete example that extracts T4 data and calculates whether an applicant qualifies for a mortgage:
async function checkMortgageEligibility(t4PdfPath, propertyPrice, downPayment) {
// Step 1: Extract T4 data
const base64 = fs.readFileSync(t4PdfPath).toString('base64');
const t4Response = await fetch('https://docusense.stackapi.dev/api/v1/documents/t4', {
method: 'POST',
headers: { 'Authorization': `Bearer ${process.env.API_KEY}`, 'Content-Type': 'application/json' },
body: JSON.stringify({ fileBase64: base64, mimeType: 'application/pdf', taxYear: 2024 })
});
const { data: t4 } = await t4Response.json();
const annualIncome = t4.boxes.box14;
// Step 2: Calculate mortgage using FinGuard API
const loanAmount = propertyPrice - downPayment;
const mortgageResponse = await fetch('https://api.stackapi.dev/api/v1/calculators/mortgage', {
method: 'POST',
headers: { 'Authorization': `Bearer ${process.env.API_KEY}`, 'Content-Type': 'application/json' },
body: JSON.stringify({
loanAmount,
interestRate: 5.5,
loanTermYears: 25
})
});
const { data: mortgage } = await mortgageResponse.json();
// Step 3: Check GDS ratio (should be under 32%)
const monthlyIncome = annualIncome / 12;
const gdsRatio = (mortgage.monthlyPayment / monthlyIncome) * 100;
return {
employeeName: t4.employeeName,
annualIncome,
monthlyPayment: mortgage.monthlyPayment,
gdsRatio: gdsRatio.toFixed(2),
eligible: gdsRatio < 32
};
}
// Usage
const result = await checkMortgageEligibility('./jean-t4.pdf', 450000, 90000);
console.log(result);
// {
// employeeName: "Jean Tremblay",
// annualIncome: 72000,
// monthlyPayment: 2134.50,
// gdsRatio: "35.57",
// eligible: false
// }
What About Scanned T4s?
Scanned T4s (image-based PDFs) are handled automatically — no extra configuration needed. The same API call works for both digital and scanned documents.
You can also send image files directly:
// Works with JPG, PNG, WEBP too
body: JSON.stringify({
fileBase64: base64,
mimeType: 'image/jpeg', // or image/png, image/webp
taxYear: 2024
})
Quebec Specifics: RL-1 Support
If you work with Quebec employees, you'll also need to process RL-1 slips (Relevé 1 from Revenu Québec). The same approach works:
const rl1Response = await fetch('https://docusense.stackapi.dev/api/v1/documents/rl1', {
method: 'POST',
headers: { 'Authorization': `Bearer ${process.env.API_KEY}`, 'Content-Type': 'application/json' },
body: JSON.stringify({
fileBase64: base64,
mimeType: 'application/pdf',
taxYear: 2024,
language: 'fr'
})
});
Returns all RL-1 cases: A (employment income), B (QPP), C (EI), E (Quebec tax withheld), G (QPP admissible salary), H/I (QPIP)...
Getting Started
- Sign up for a free API key at RapidAPI — DocuSense API
- The free tier includes 100 documents/month — enough to test thoroughly
- T4 extraction requires the PRO plan ($19/month)
Summary
| Approach | Setup time | Maintenance | Scanned PDFs |
|---|---|---|---|
| Tesseract OCR + custom parser | 2-3 days | High | Poor |
| AWS Textract | 1 day | Medium | Good |
| Google Document AI | 1 day | Medium | Good |
| DocuSense API | 10 minutes | Zero | Yes |
If you're building any Canadian fintech workflow that touches T4s — mortgage applications, payroll software, accounting tools, income verification — this will save you significant development and maintenance time.
Have questions about the API or want to share what you're building? Drop a comment below.