Mitsui Chemicals HRMS
Payroll & Attendance Management System
Project Overview
Mitsui Chemicals required a digital HRMS for their regional operations to replace a legacy payroll system that required manual intervention for every pay cycle. The system needed to handle Japanese taxation rules, region-specific allowances, and integrate with physical time-tracking hardware on the factory floor.
What We Were Solving
The existing payroll process required five HR staff members to manually calculate each employee's gross pay, apply the correct tax brackets, account for overtime and allowances, and then cross-check everything before payment — every month. Errors were common, corrections were expensive, and the process routinely took two full work weeks. Attendance was tracked via paper punch cards that were manually entered into a spreadsheet.
How We Built It
We built a full-stack HRMS with Django/PostgreSQL on the backend and a React dashboard on the frontend. The payroll engine implements a declarative rule system for tax brackets, allowances (housing, travel, meal, dependents), and deductions, configurable per employee grade and region without code changes. The attendance module integrates with IP-based time-clock hardware via API, automatically calculating hours worked, overtime tiers, and leave balances. A bulk salary review workflow allows HR to approve pay adjustments for entire departments in one action.
Engineering Decisions
Declarative Payroll Rules Engine
Tax bands, allowances, and deductions are configured via an admin interface — not hardcoded. HR can update rules as regulations change without requiring a developer, and the system auto-applies changes to the next pay cycle.
Hardware-Integrated Attendance
The system polls time-clock hardware via a secure local API adapter, ingesting raw punch data and computing shift durations, overtime tiers, and late arrivals automatically — no manual entry required.
Bulk Review Workflow
A structured approval workflow lets HR managers review, adjust, and approve salary changes for entire departments simultaneously, with complete change history and a one-click payroll run trigger.
External Audit Verification
The payroll output was verified by the client's external auditor after the first three months of operation and received a clean bill — no discrepancies found across 800+ employee records.
The system delivered exactly what it promised. Our payroll now runs in two days with no errors, and the attendance data feeds automatically. The HR team has reclaimed weeks of their time every month.
Key Results
Tech Stack
In Action
Declarative payroll engine handling tax brackets, allowances, and deductions
One-click payslip generation with full itemised breakdown
Hardware-integrated punch-based attendance with overtime calculation