Quarterly Tax Calculator
Last reviewed 30 September 2026
Added the next payment under the IRS regular installment method (Pub. 505): an even split underpays the next period after a mid-year increase. Checked against the IRS example, $1,800 refigured to $4,100 after $900 paid: $2,175, then $1,025.
Home Improvement Value Calculator
Last reviewed 27 September 2026
Tested that every preset reproduces the report’s published cost-recouped percentage and that the value added scales with the cost entered.
Loan Payoff Calculator
Last reviewed 27 September 2026
Checked against OpenStax Principles of Finance 8.3 (Tables 8.4 and 8.5, and the $2,000 prepayment), where the schedule shows the prepaid mortgage ending about four and a half months early rather than the six the text gives.
Production Possibilities Frontier Calculator
Last reviewed 27 September 2026
Checked against OpenStax’s published straight-frontier figures (a burger costs four bus tickets; a ticket 0.25 burgers, then 0.50) and against the frontier’s own geometry on eight shapes.
Nash Equilibrium Calculator
Last reviewed 27 September 2026
Checked against OpenStax Principles of Economics Tables 10.2 and 10.3, and against the definition of equilibrium itself in 4,000 random games.
Price Ceiling and Floor Calculator
Last reviewed 27 September 2026
Runs on the Market Equilibrium Calculator’s engine; checked against OpenStax’s rent-control example (Table 3.7: a $500 ceiling, 15,000 supplied against 19,000 demanded) and against the deadweight-loss triangle in 3,000 random markets.
Tax Incidence Calculator
Last reviewed 27 September 2026
Runs on the Market Equilibrium Calculator’s engine; checked against OpenStax’s rule that the more inelastic side bears more of the tax, in 3,000 random markets.
Working Hours Calculator
Last reviewed 27 September 2026
Published the working hours calculator: working time across spans, shifts and time zones, with daylight-saving transitions handled from the IANA database.
Business Days Calculator
Last reviewed 27 September 2026
Published the business days calculator: weekday counting with published public-holiday data per region, a reverse mode, and a month-by-month breakdown.
Lakh and Crore Converter
Last reviewed 27 September 2026
Released on 27 September 2026, with a title that begins with the page heading and the Number Scale Converter linking to it for readers who count in lakh and crore.
Torque Converter
Last reviewed 27 September 2026
Also covers what a converted figure cannot carry: dry-versus-lubricated threads change clamping force by 20–30% at the same reading, torque-to-yield fasteners are single-use, and a wrench measures applied effort rather than the clamping force that holds the joint.
Decibel Calculator
Last reviewed 27 September 2026
Verified by 76 automated cases, including that combine and the n-identical-sources shortcut agree, and that every doubling of distance costs 6.02 dB from any starting point.
Frequency to Wavelength Converter
Last reviewed 27 September 2026
Every constant is exact by the 2019 SI definitions, so the conversions are exact arithmetic. Verified by 92 automated cases including round-trips through both the medium and vacuum wavelengths for six media at four frequencies.
Real Wage Calculator
Last reviewed 27 September 2026
Published the real wage calculator: two paychecks from different years compared on the BLS CPI-U, the pay that would have kept pace, the real raise from any raise and inflation rate, and the real-wage formula in 1982-84 dollars.
CAGR Calculator
Last reviewed 27 September 2026
Published the CAGR calculator: the compound annual growth rate between two values, plus the end value a rate reaches and the years it needs, with the year-by-year path, the simple-average and rule-of-72 comparisons, and cases checked against the 2020 Census and an OpenStax textbook problem.
Rule of 72 Calculator
Last reviewed 27 September 2026
Published the rule of 72 calculator: years to double from a rate or the rate to double in a set time, with the exact answer and the error beside the rule, the rules of 70, 69.3, 114 and 144, and the OpenStax textbook case checked.
Employee Cost Calculator
Last reviewed 27 September 2026
Tested employer FICA against the 2026 Social Security wage base, the FUTA figures against IRS Topic 759, and the calculator on BLS full-time shares against the 1.31 multiplier BLS measured.
VA Loan Calculator
Last reviewed 26 September 2026
Tested against VA's own examples ($10,000 down on a $200,000 home pays a $2,850 fee; $175,000 of remaining entitlement supports a $700,000 loan with no down payment), the fee band edges at exactly 5% and 10% down, and 300 random loans for the exemption, the monthly total and the cost of financing the fee.
Income Tax Calculator
Last reviewed 26 September 2026
Became the US federal income tax calculator (2026 and 2025 IRS figures) when the UK, India, Australia and Canada moved to their own calculators: the country presets, the custom-band modes and the UK and India sections are gone, and the page now shows the 2026 brackets for every filing status, the standard deduction, and single-filer examples on 2026 figures (they had used the 2025 brackets).
Salary & Take-Home Pay Calculator
Last reviewed 26 September 2026
Canada: income tax now follows the CRA's annual T4127 formulas and, for Quebec, Revenu Québec's rules. The Canada employment amount is credited, only the base part of CPP earns a credit while the enhanced part and CPP2 are deducted from income, Ontario's Health Premium and tax reduction and BC's tax reduction are included, Manitoba's and Yukon's personal amounts phase down with income, and Quebec tax uses the deduction for workers with no separate contribution credits. Checked against the CRA's and Revenu Québec's published maximums and an independent implementation of the formulas.