Calculator Matters Changelog

Every calculator on this site tracks its own real edit history — not just a silent "Updated" date. This page lists every calculator that has one, most recently changed first. The same history is also visible on each calculator's own page, under "What's changed."

Consumer Surplus Calculator

Last reviewed 18 August 2026

Published with the formula, a worked example, and an FAQ.
Added visual result charts.
Reviewed the formula and assumptions for accuracy.

Producer Surplus Calculator

Last reviewed 18 August 2026

Published with the formula, a worked example, and an FAQ.
Added visual result charts.
Reviewed the formula and assumptions for accuracy.

Deadweight Loss Calculator

Last reviewed 18 August 2026

Published with the formula, a worked example, and an FAQ.
Added a downloadable Excel/CSV workbook generated from your inputs.
Added visual result charts.
Reviewed the formula and assumptions for accuracy.

Gratuity Calculator

Last reviewed 16 August 2026

Published the India gratuity calculator with the 15/26 formula, per-year accrual, and Payment of Gratuity Act 1972 sourcing.

UAE Gratuity Calculator

Last reviewed 16 August 2026

Published the UAE end-of-service gratuity calculator with the 21/30-day formula, statutory 2-year cap, and Federal Decree-Law No. 33 of 2021 sourcing.

Freelancer vs Employee Calculator

Last reviewed 16 August 2026

Published the freelancer-vs-employee rate calculator: required freelance hourly/day rate to match a target salary, accounting for business expenses, lost benefits, self-employment tax, and realistic billable hours.

Real Estate Investment Calculator

Last reviewed 16 August 2026

Published the real estate investment calculator: total ROI, annualized return, cash-on-cash, and equity build-up from cash flow, principal paydown, and appreciation.

Tip Calculator

Last reviewed 16 August 2026

Published the tip calculator with bill amount, tip percentage, and per-person split.

Comparative Advantage Calculator

Last reviewed 16 August 2026

Published with the formula, a worked example, and an FAQ.

Rent vs Buy Calculator

Last reviewed 15 August 2026

Published with the formula, a worked example, and an FAQ.

Car Lease vs Buy Calculator

Last reviewed 15 August 2026

Published with the formula, a worked example, and an FAQ.

Debt Consolidation Calculator

Last reviewed 15 August 2026

Published with the formula, a worked example, and an FAQ.

Debt Payoff vs Investing Calculator

Last reviewed 15 August 2026

Published with the formula, a worked example, and an FAQ.

Mortgage Calculator

Last reviewed 8 August 2026

Published the mortgage payment calculator with formula and amortization.
Added a lender/offer comparison and a deeper affordability check.
Added a decision receipt and reviewed assumptions for accuracy.
Tightened the SERP title and opening copy for monthly-payment search intent, aligned the JSON-LD title/description to match the rendered page exactly, followed the CFPB/Freddie Mac citations instead of nofollowing them, and memoized the 9-scenario comparison panel to stop it recomputing on unrelated UI interactions.

Days Calculator

Last reviewed 7 August 2026

Published the Days Calculator: days between two dates with a calendar breakdown, add/subtract days, and business days excluding weekends and a custom holiday list.
Leap years are handled via date-object arithmetic, not a fixed 365-day approximation.
Corrected taxonomy: moved from Math & Statistics to Time & Date (its actual primary user intent) and migrated the URL from /math/days-calculator/ to /time-date/days-calculator/ with a 301 redirect, since the page was 2 days old and not yet indexed.

Global Import Duty Calculator

Last reviewed 6 August 2026

Published the Global Import Duty Calculator: shipment value, freight, and insurance to duty, tax, and total landed cost, in a generic mode for any country, plus a sourced India mode (Basic Customs Duty, Social Welfare Surcharge, and IGST per CBIC Circular No. 3/2022).
Added as the Tax category's fourth tool alongside the Income Tax, VAT/GST, and Salary & Take-Home Pay calculators.

DDP vs DAP Cost Calculator

Last reviewed 6 August 2026

Published the DDP vs DAP Cost Calculator: compares buyer landed cost for an international shipment under Incoterms 2020 DAP (Delivered at Place) and DDP (Delivered Duty Paid), from goods value, freight, insurance, duty rate, duty basis (CIF or FOB), tax rate, clearance fee, and a DDP handling fee, plus a DAP/DDP/DDU/FCA/CIF comparison table.
Added as the Business & Ecommerce category's ninth tool alongside Profit Margin, Markup, Break-Even, Ecommerce Profit, Break-Even ROAS, LTV:CAC, Price Elasticity of Demand, and AI Agent Cost calculators.

Roofing Calculator

Last reviewed 6 August 2026

Published the Roofing Calculator: a Roof Area & Squares mode (footprint length/width and pitch to pitch multiplier/angle/grade, roof surface area, and roofing squares with a waste allowance) and a Materials & Cost mode (shingle bundles, metal panel area with an independent sheet-weight calculator, or flat-membrane area, plus an estimated installed cost).
Added as the Home & Energy category's fourth tool alongside the Solar Panel Roof-Fit Calculator, the Gutter Calculator, and the Insulation Calculator.

Decking Calculator

Last reviewed 6 August 2026

Published the Decking Calculator: deck length/width to board count, joist count, and fastener count (face-screwed or hidden clips), in feet/inches or metres/millimetres, with an optional material cost estimate.
Added as the Home & Energy category's fifth tool alongside the Solar Panel Roof-Fit Calculator, the Gutter Calculator, the Insulation Calculator, and the Roofing Calculator.

Fence Calculator

Last reviewed 6 August 2026

Published the Fence Calculator: a Posts, Rails & Pickets mode (length/height/spacing/gates to post count and buried post length, rail count, picket/board count with waste and an optional board-on-board overlap, and concrete bags) and a Materials & Cost mode (region-aware cost for wood, vinyl, or chain-link, chain-link mesh area/rolls/line posts, and a stain-coverage calculator).
Added as the Home & Energy category's sixth tool alongside the Solar Panel Roof-Fit Calculator, the Gutter Calculator, the Insulation Calculator, the Roofing Calculator, and the Decking Calculator.

Time Zone Converter

Last reviewed 5 August 2026

Published the Time Zone Converter, computing conversions live from the browser's IANA time zone database with automatic daylight-saving handling and a multi-zone world clock view.
Launched Calculator Matters' Time & Date category with this calculator as its first tool.

Timesheet Calculator

Last reviewed 5 August 2026

Published the Timesheet Calculator: a weekly, biweekly, or monthly clock-in/clock-out grid with unpaid-break deduction, automatic overnight-shift handling, decimal and hours:minutes totals, an optional overtime threshold, and an Excel export.
Added as the Time & Date category's next tool alongside the Time Zone Converter.

Age Calculator

Last reviewed 5 August 2026

Published the Age Calculator: exact age in years/months/days from a date of birth as of any date, total days/weeks/months/hours lived, day of the week born, a next-birthday countdown, and Excel/SQL/PHP/Java/Oracle/Access/SAS formula references.
Added as the Time & Date category's next tool.

Time Percentage Calculator

Last reviewed 5 August 2026

Published the Time Percentage Calculator: percentage-of-a-total and percentage-change modes across seconds, minutes, hours, and days, an hour-breakdown quick-reference table, and an Excel/Sheets formula section.
Added as the Time & Date category's next tool alongside the Time Zone Converter.

Solar Panel Roof-Fit Calculator

Last reviewed 5 August 2026

Published the Solar Panel Roof-Fit Calculator: roof area to system size and panel count, estimated generation, cost/incentive/payback, and an optional EMI, with built-in defaults for India (PM Surya Ghar subsidy), the USA, and the UK.
Launched Calculator Matters' Home & Energy category with this calculator as its first tool.

Gutter Calculator

Last reviewed 5 August 2026

Published the Gutter Calculator: a sizing mode (roof area and rainfall intensity to required flow, US K-style recommendation, downspout count, slope/fall) and a materials-and-cost mode (run length to sections, hangers, downspouts, coil stock, and installed cost), with SMACNA (USA), AS/NZS 3500.3 (Australia/NZ), and BS EN 12056-3 (UK) methods.
Added as the Home & Energy category's second tool alongside the Solar Panel Roof-Fit Calculator.

Insulation Calculator

Last reviewed 5 August 2026

Published the Insulation Calculator: area and target R-value to depth needed and quantity to buy, across blown-in (fiberglass, cellulose, mineral wool), batt/roll/rigid-board (fiberglass, mineral wool, XPS foam board), and spray foam (open- and closed-cell) formats, with an optional material cost estimate.
Added as the Home & Energy category's third tool alongside the Solar Panel Roof-Fit Calculator and the Gutter Calculator.

TDEE Calculator

Last reviewed 21 July 2026

Published the TDEE calculator: Mifflin-St Jeor BMR/TDEE engine, five activity levels, maintenance range, and weight-loss/weight-gain calorie scenarios.
Added as the Health category's second tool, wired to the same containment policy as BMI (noindex,follow) pending Health's reindexing gate.

Calorie Deficit Calculator

Last reviewed 21 July 2026

Published the Calorie Deficit & Weight Loss Timeline calculator: adaptive week-by-week projection, faster/central/slower planning range, scenario comparison, and a 1,200 cal/day safety-floor caution.
Added as the Health category's third tool, wired to the same containment policy as BMI (noindex,follow) pending Health's reindexing gate.

AI Agent Cost Calculator

Last reviewed 16 July 2026

Published the AI Agent Cost Calculator: multi-model stack, prompt caching, agent trajectory, retry/failure economics, human review, fixed and amortised implementation cost, scenario comparison, and cost-range uncertainty modelling.
Cost per successful task (not cost per attempt) is the calculator's core metric, computed from retry mathematics rather than a naive token multiplication.

BMI Calculator

Last reviewed 14 July 2026

Published the BMI calculator with metric and imperial formulas, adult WHO/CDC category bands, and a healthy-weight range.
Launched Calculator Matters' Health category with this calculator as its first tool.

Salary & Take-Home Pay Calculator

Last reviewed 2 July 2026

Published with the formula, a worked example, and an FAQ.
Added a downloadable Excel/CSV workbook generated from your inputs.
Added side-by-side scenario comparison.
Added an advanced, multi-mode planner.
Reviewed the formula and assumptions for accuracy.
Clarified guidance wording to point to employer payroll and tax-authority tools for consequential decisions.

Investment Calculator

Last reviewed 22 June 2026

Published with the formula, a worked example, and an FAQ.
Added a downloadable Excel/CSV workbook generated from your inputs.
Added visual result charts.
Added side-by-side scenario comparison.
Added an advanced, multi-mode planner.
Reviewed the formula and assumptions for accuracy.
Added a "use this vs. another calculator" guide, neutralised scenario wording, and refreshed the review date.

Loan Calculator

Last reviewed 20 June 2026

Published with the formula, a worked example, and an FAQ.
Added a downloadable Excel/CSV workbook generated from your inputs.
Added a full payment-by-payment schedule.
Added a Loan Eligibility / borrowing-capacity mode (income, existing EMIs, FOIR/DTI, rate, tenure) with scenario comparison, a chart, and a dedicated Excel report.
Reviewed the formula and assumptions for accuracy.

Income Tax Calculator

Last reviewed 20 June 2026

Published with the formula, a worked example, and an FAQ.
Added a downloadable Excel/CSV workbook generated from your inputs.
Added side-by-side scenario comparison.
Added region-specific modes and labels.
Added an advanced, multi-mode planner.
Corrected the country-support wording to clearly separate built-in official modes (US, UK, New Zealand, India, UAE) from the custom tax-band mode, and marked Canada and Australia as coming soon. Added a compact trust row and a built-in/custom/coming-soon coverage strip.
Reviewed the formula and assumptions for accuracy.

Savings Calculator

Last reviewed 15 June 2026

Published with the formula, a worked example, and an FAQ.
Added a downloadable Excel/CSV workbook generated from your inputs.
Added visual result charts.
Reviewed the formula and assumptions for accuracy.

Retirement Calculator

Last reviewed 15 June 2026

Published with the formula, a worked example, and an FAQ.
Added a downloadable Excel/CSV workbook generated from your inputs.
Added visual result charts.
Reviewed the formula and assumptions for accuracy.

Regular Investment Calculator

Last reviewed 15 June 2026

Published the regular-investment (SIP/DCA) projector with future value and inflation.
Added step-up, cost-of-delay, risk-range, contribution-pause and lump-vs-recurring modules.
Reviewed the projection formula for accuracy.

Retirement Withdrawal Calculator

Last reviewed 15 June 2026

Published the retirement-withdrawal (drawdown) calculator with depletion year and withdrawal rate.
Added a sequence-of-returns risk simulator and a decision receipt.
Reviewed the drawdown mechanics for accuracy.

ROI Calculator

Last reviewed 15 June 2026

Published with the formula, a worked example, and an FAQ.
Added a downloadable Excel/CSV workbook generated from your inputs.
Added visual result charts.
Added side-by-side scenario comparison.
Reviewed the formula and assumptions for accuracy.

Dividend Reinvestment Calculator

Last reviewed 15 June 2026

Published with the formula, a worked example, and an FAQ.
Added a downloadable Excel/CSV workbook generated from your inputs.
Added visual result charts.
Added side-by-side scenario comparison.
Reviewed the formula and assumptions for accuracy.

Scientific Calculator

Last reviewed 15 June 2026

Published the scientific calculator: trigonometry (degrees/radians), logarithms, powers, roots, factorials, parentheses and percentages.
Added memory registers, a saved history, keyboard entry, and an adversarially-tested expression engine.
Reviewed order-of-operations and domain handling for accuracy.

Standard Deviation Calculator

Last reviewed 15 June 2026

Published the descriptive-statistics analyzer (sample/population SD, variance, quartiles, z-scores, outliers).
Added skewness and excess kurtosis, Cohen’s d with pooled SD, and a chi-square confidence interval for σ/σ².
Reviewed every formula against Excel/HyperFormula for accuracy.