Professional Tax (PT) in India is levied by individual states, each with its own slab schedule, deduction periodicity (monthly, half-yearly, or annual), rounding rules, and challan/return formats. ERPNext core lets you attach a generic Salary Component and a fixed formula to a Salary Structure, but it has no concept of a state-driven slab table that changes by fiscal year, no built-in logic to pick the right slab based on an employee's work state, and no PT return or challan dataset to hand your compliance team. Payroll officers end up maintaining spreadsheets of state slabs, hard-coding conditions into Salary Component formulas, and manually reconciling deductions at return-filing time — which breaks the moment a state revises its schedule or an employee transfers between locations.

We build a proper Frappe app (its own module, not a customization dumped into the site) that models this correctly. A Professional Tax Slab DocType holds per-state, fiscal-year-versioned slab rows (income band from/to, PT amount, and the deduction month(s) that state collects in), with a parent PT State Configuration DocType capturing the collecting authority, employer registration number, and return frequency. A child structure links each employee's applicable state (resolved from the Employee's work location / branch), and the deduction amount is computed at payroll run time rather than baked into a static formula. This means a Maharashtra employee correctly gets the February-loaded higher slab while a Karnataka employee is deducted every month — from the same Salary Structure.

Technically, the deduction is injected into Salary Slip via a hooks.py doc event (before_validate / on_submit) backed by a server-side calculation method, so the PT component reflects the correct versioned slab for the payroll period's fiscal year. A scheduler event runs a periodic reconciliation that aggregates submitted slips into a PT Return document per state and period, producing the challan-ready dataset (employee count by slab, total PT payable, employer split) your team exports for filing. Whitelisted methods exposed over the Frappe REST API let your finance tooling pull PT summaries programmatically; client scripts on the Salary Structure and Employee forms give payroll staff inline slab previews; and role profiles plus DocType permissions keep slab maintenance restricted to a Payroll Manager while officers only run and view.

Because this is build-to-order, nothing ships until we agree on scope. We start with a short scoping call to confirm which states you operate in, your ERPNext version (v15 or v16), your Salary Structure conventions, and your return-filing workflow. We then build against your requirements, deliver installable source code and documentation, validate on a staging copy of your site with real UAT data, and hand over the git repository. Typical delivery is one working week from confirmed scope, and every engagement includes a post-go-live support window.