Methodology & Calculation Notes

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This page documents core formulas, assumptions, and limitations used in Upaman calculator tools. Results are informational estimates and not legal, tax, investment or accounting advice.

Scope

Indian calculators: EMI, SIP, PPF, GST, Income Tax, Salary, Credit Card Trap, IRCTC booking utility, Age.
US calculators: Mortgage, Refinance, Auto Loan, 401(k), Savings/CD, Credit Card Payoff.
EU/UK calculators: UK Income Tax, EU VAT, European Salary, Germany/France/Netherlands salary, UK Rail utility.
Guided workflows: Job Offer Decision and Home Loan Readiness (region-aware models).

Formula Highlights

Loan EMI: EMI = P*r*(1+r)^n / ((1+r)^n - 1), where r = annualRate/12.

SIP future value: monthly compounding with optional step-up contributions.

PPF projection: contribution-mode-based monthly accrual approximation with annual interest crediting.

GST add/remove: add uses amount * rate; reverse uses inclusive * 100 / (100 + rate).

Tax calculators: slab-wise marginal application with cess/rebate logic as configured in each tool.

Credit card trap: month-wise amortization using APR/12, minimum due guardrails and fixed-payment comparison.

Salary tools: approximate structures and deduction assumptions are explicitly listed in each calculator.

Guided Workflow Models

Job Offer Decision Workflow: compares current vs new annual compensation, estimates annual tax and local deductions with region presets, and adjusts monthly gain by location cost index. Output includes affordability-based allocation suggestions and decision flags.

Home Loan Readiness Workflow: computes safe housing budget using risk profile (FIOR cap + buffer), derives safe EMI after estimated ownership overhead, and compares against required EMI for target property and tenure.

Regions supported: India, United States, EU/UK (generic). Region changes affect currency format, default assumptions, and recommendation thresholds.

Data and Update Policy

Rules and rates are updated when official policy announcements are confirmed.
Market/news widgets rely on periodic static JSON updates and external data feeds where applicable.
UK rail utility may use live API data or controlled fallback responses when API access is unavailable.

Known Limitations

Regional workflow models are planning approximations and not substitutes for country-specific tax filing or lender underwriting.
Jurisdiction-specific exceptions, special exemptions, and edge-case tax situations may not be fully represented.
Real lender products, fund performance, and statutory guidance can differ from model assumptions.
Users should validate critical decisions using official portals and licensed professionals.

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