Sources & References

Our calculators implement standard, published rules and formulas rather than proprietary models, so the figures can be independently verified. This page lists the authoritative sources we rely on for the rates and rules that change over time, and explains how we cite and check them. It complements our methodology, which sets out the formulas themselves.

Primary sources

For any figure set by a rule or rate — a tax slab, a statutory GST rate, the PPF rate, a benchmark lending rate — we defer to the body that publishes it:

• Reserve Bank of India (RBI) — Repo rate and the external-benchmark lending-rate framework that underpins floating loan rates, and general guidance on how banks compute interest.
• Income Tax Department, Government of India — Income-tax slabs, the Section 87A rebate, surcharge thresholds and cess for both the old and new regimes, by financial year.
• Goods and Services Tax Council / CBIC — The statutory GST rate slabs and the CGST / SGST / IGST split used by the GST calculator.
• National Savings Institute / India Post — Small-savings scheme rules and interest rates, including PPF, used by our savings calculators.
• Standard financial mathematics — The reducing-balance EMI formula, compound-interest and annuity formulas, and the present-value / internal-rate-of-return methods (including the actual/365 XIRR convention) that our investment engines implement.

How we cite and verify

• Defer to the primary source. Where an official figure exists, we use it directly rather than relying on secondary reporting.
• Version the figures that change. Rates and rules that change with the Budget or a regulator's decision are stored in typed data files keyed by period (for example, tax data by financial year), so each figure is traceable and dated.
• Reconcile on review. During review we re-check rule-based figures against the source listed above, and we update the page's reviewed date once confirmed.
• Label estimates. Outputs that depend on assumptions (a constant rate, no fees) are presented as estimates, and the assumptions are stated in our methodology and disclaimer.

A note on accuracy of external figures

Official rates and rules can change, and there can be a short lag between an announcement and our update. We treat tax and rate figures as point-in-time and prioritise updating them when they change. If you are making a decision that hinges on an exact current figure, confirm it with the relevant institution or its official website before acting.

Suggest a correction or source

If you believe a figure is out of date, or you can point us to a better primary source, email contact@freeemicalculator.com. We welcome it — accurate sourcing is core to what this site is for.