How we calculate
The sources, formulas and assumptions behind every BlogBanking calculator, and how we keep them up to date.
Last updated 18 October 2026
Sources we rely on
We base our calculators on official, primary sources wherever they exist:
- Income Tax Department: the Income-tax Act, 2025, the Income-tax Rules, 2026 and Finance Acts.
- Union Budget documents for rate changes.
- CBIC and the GST Council for GST rates.
- Reserve Bank of India for lending rules.
- EPFO for provident fund rules.
Formulas by calculator
| Calculator | Method |
|---|---|
| EMI | Reducing-balance EMI, simulated month by month for prepayments and rate changes |
| Income tax | Slab tax for the old and new regime, rebate, marginal relief, surcharge with marginal relief, 4% cess |
| Salary | CTC less employer PF and gratuity, then your PF, professional tax and income tax |
| HRA | Least of HRA received, rent minus 10% of salary, and 50% or 40% of salary by city |
| GST | Exclusive and inclusive GST, split into CGST and SGST or IGST |
Assumptions and limits
- Tax tools cover resident individuals and income taxed at slab rates. Special-rate income such as capital gains is not included.
- Salary structures vary by employer. We use a typical split, which you can adjust.
- Loan results exclude processing fees, insurance and broken-period interest unless stated.
- GST rates depend on the exact HSN or SAC code of a product or service.
- Amounts are rounded to the nearest rupee for display.
Testing and review
Every formula is tested against worked examples from official sources and well-known published figures before a tool goes live. For example, the income tax engine must return ₹0 on a ₹12.75 lakh salary and ₹1,09,200 on ₹15.75 lakh under the new regime for FY 2026-27.
We review the tax and GST tools after every Union Budget, Finance Act and notified rule change, and each tool page shows the date it was last reviewed.
Corrections
If you find a mistake, please email hello@blogbanking.com with the inputs you used and the result you expected. We fix confirmed errors as a priority and update the review date.