How we check the calculators

What we check

Every change to the calculators runs two sets of automated checks before it goes live. They are engineering checks of the maths and the pages, not a professional review of every financial situation.

The maths

• Tax at the edge of every slab in both regimes, and the rebate limits (₹12 lakh of taxable income in the new regime, ₹5 lakh in the old) with marginal relief just above them, including for freelancers, who get no standard deduction.
• Surcharge at each threshold with its marginal relief, 4% cess, rounding to the nearest ₹10, and that tax never goes down as income goes up, from ₹0 to ₹6 crore.
• Zero and negative returns: a 0% return gives back exactly what you put in, the lower-return check never drops below 0%, and when returns trail inflation the page says plainly that the target isn't reached.
• Zero-interest EMIs, and loan accounting: every rupee paid is either loan or interest, the balance only falls and ends at zero, and prepayments shorten the loan.
• Dollar-to-rupee conversions for RSUs at the vest and sale rates, with paise kept until the final figure, including a gain or loss from the exchange rate alone.
• The ₹10,000 point at which advance tax starts, and the amounts due by each date.
• Each calculator's worked example against the official rules, and every calculator at the edges of its inputs, with no blank or broken figures.

In a browser, at phone and desktop sizes

• Every calculator loads, shows a result and updates as you type or change a choice, with no errors.
• Inputs: amounts that are out of range or empty are flagged, and letters can't get into number boxes.
• Shared links: numbers in a link fill the calculator in, numbers out of range are pulled back inside it, and "Share with a friend" sends the plain page link, never your numbers.
• Amounts in words, and the pop-ups that explain money terms and link forms to their official pages.
• Layouts from a 360px phone to a 1440px desktop, with nothing scrolling sideways.

Rates, dates and tax scope

• The tax calculators are for tax year 2026-27 (FY 2026-27, AY 2027-28), for resident individuals below 60, with income taxed at slab rates: salary, interest, rent or freelance profit.
• They include the standard deduction, the rebate with marginal relief, surcharge above ₹50 lakh with its marginal relief, and 4% cess. Deductions you enter are taken as eligible and within their limits.
• They leave out income taxed at special rates, such as capital gains. The RSU calculator is the one exception: it works out the tax on selling the shares at their own rates, without surcharge on the gain.
• The PPF and Sukanya Samriddhi pages say which period their rate is for (October to December 2026 now), and you can change the rate.
• “Checked 5 November 2026” is when the rules were last checked. A rate's period, such as October to December 2026, is when the government applies it. The two dates are separate.
• Default returns (10% a year, also shown 2 points lower), the 3.5% withdrawal rate and 6% inflation are assumptions you can change, not forecasts.

Rounding and model differences

• Money totals are shown in whole rupees. Income tax is rounded to the nearest ₹10, as the law says. Short forms such as ₹40.68 lakh are rounded for easy reading.
• Exchange rates keep their paise and dollar prices their cents, and every calculation keeps full precision until the final figure.
• Real figures can differ. Lenders work interest out daily and may round an EMI up; fees, insurance and GST add to a loan's cost; payroll can withhold tax differently; and real investments never return the same amount every year.

Who checks the rules

The rules, rates and default assumptions are checked against official texts by Prashanth Sekhar, who updates them every quarter and after each Budget. Each calculator shows the date they were checked and links its sources.

Spotted a wrong number? Tell us and we'll check it.

All calculators