Legal & Tax IntelligenceOctober 8, 20268 min read

Deterministic Personal & Corporate Tax Engineering: Modeling IT-10B Wealth Statements, Schedule 2 Rebates & Payer TDS Under the Income Tax Act 2023

Why LLMs must never do tax math: how Zunn Legally pairs neural legal understanding with deterministic calculation engines to compute Personal Tax, IT-10B wealth statement reconciliations, and corporate TDS withholding.

Mahbubur Rahman, LL.M.

Lead Legal Knowledge Systems Engineer

1. The LLM Arithmetic Failure

Large language models are probabilistic sequence predictors. When asked to calculate personal income tax involving progressive tax slabs, investment rebate ceilings, and net wealth surcharges, LLMs produce rounding errors, invert bracket ceilings, and hallucinate final tax payable numbers.

Tax assessment under the Bangladesh Income Tax Act 2023 is a strictly deterministic mathematical operation. A single misplaced digit in an IT-10B wealth reconciliation statement triggers an audit notice under Section 163.

Zunn Legally completely separates language parsing from computational arithmetic. The AI extracts financial line items from salary slips, bank statements, and trial balances; a deterministic TypeScript/Rust mathematical engine executes the computation.

2. Personal Tax & Slabs Engine

Under the Income Tax Act 2023, individual income computation requires sequential evaluation of salary perquisites (rent exemption formulas, medical allowances), house property income, capital gains, and allowable deductions.

Legally evaluates all progressive tax brackets (from 0% up to 25% or 30%) and applies investment tax rebate rules under the Second Schedule with exact ceiling caps (15% of eligible investments or 3% of total taxable income).

Deterministic Tax Slab Calculator Interface

interface TaxCalculationResult {
  grossIncome: number;
  exemptIncome: number;
  taxableIncome: number;
  bracketBreakdown: Array<{ slab: string; rate: number; taxAmount: number }>;
  grossTax: number;
  allowableRebate: number;
  netTaxPayable: number;
  surchargeAmount: number;
  finalLiability: number;
  auditTrail: string[];
}

3. Algorithmic IT-10B Wealth Statement

The Form IT-10B (Statement of Assets, Liabilities, and Expenses) requires mathematical balance: Beginning Net Wealth + Total Accretion of Wealth (Savings + Capital Gains + Inheritances) - Family Expenditure must equal Ending Net Wealth down to the last Taka.

Legally automatically extracts asset entries (real estate, motor vehicles, shares, bank balances) and cross-reconciles discrepancies in real time, alerting practitioners to unreconciled gaps before filing.

Income Tax Act 2023Section 78 & Rule 14

Mandatory filing of Statement of Assets and Liabilities (Form IT-10B) and wealth surcharge thresholds.

4. Corporate TDS & Section 55

For enterprise finance teams, payer-side Tax Deducted at Source (TDS) is a major liability zone. Failure to deduct accurate TDS under Section 52 results in complete disallowance of the underlying expense under Section 55, triggering immediate corporate tax additions.

Legally's Corporate TDS engine inspects vendor invoices, determines the statutory deduction rate based on 12-digit e-TIN verification and PSR submission status, and computes the exact withholding amount.

5. Generating Audit-Ready Tax Packs

Once computed, Legally generates comprehensive, audit-ready tax filing packages complete with mathematical reconciliation traces, statutory references, and supporting document schedules.