Every calculator on this site is only as honest as the figures behind it. This page lists, category by category, where those figures come from, how we turn them into a tool, and — just as important — which numbers are not official figures at all, but estimates from a model whose assumptions we state.
How to read the labels on this page: [cited] means the site’s own content already names this source today. [governing] means this is the body that actually publishes the figure the tool uses. Where no authority publishes the figure, the page says so.
Our rules
Official source first. When a government body, regulator or standards body publishes the figure — a tax bracket, a loan limit, a benefit table — we take the figure from that source and say which one it is, on this page and, where it matters, on the tool page itself.
The worked example is the audit trail. Every tool page shows its formula and a worked example with real inputs, so you can check the tool’s answer against the example yourself before you trust it with your own numbers.
Projections are labelled as projections. When a figure is a forecast — next year’s premium, a projected rate — the page says so next to the number, with the name of the body that published the projection.
Your figures never leave your device. Every tool runs in your browser. Nothing you type is uploaded, stored or seen by us, which is also why the site needs no account.
Corrections outrank new features. When an official figure changes, the affected defaults are updated. When a reader reports an error and it checks out, it is fixed and the page’s “Last updated” date moves — that date only ever moves when the content actually changes.
Mortgage & Housing
Figure
Source
Default mortgage rates
Freddie Mac, Primary Mortgage Market Survey (PMMS) — the survey the site’s defaults track (30-year fixed averaged 7.40% in the mid-October 2026 survey the current defaults rest on). [cited]
FHA loan limits and mortgage insurance premiums
U.S. Department of Housing and Urban Development (HUD) — the 2026 FHA limits the housing tools work inside run from a floor of $541,287 to a high-cost ceiling of $1,249,125. [cited]
VA loan funding fees and entitlement rules
U.S. Department of Veterans Affairs (VA) published funding-fee tables. [governing]
Conforming loan limits
Federal Housing Finance Agency (FHFA) annual limit announcements. [governing]
PMI cancellation rights
The Homeowners Protection Act (PMI Act), administered with Consumer Financial Protection Bureau (CFPB) guidance. [governing]
Everyday Money
Figure
Source
Social Security cost-of-living increase
Social Security Administration (SSA) — the COLA Calculator applies the 3.6% increase the SSA announced. [cited]
Trump Accounts rules and limits
The Internal Revenue Service (IRS) guidance on the programme. [cited in the tool’s template]
Federal pay brackets behind the Paycheck Calculator
IRS federal withholding brackets and the standard deduction for the stated tax year. [cited]
Loan, EMI, payoff and budget figures
No official source — estimate model. These tools apply the standard amortisation and budgeting mathematics to the figures you enter. EMI conventions follow the reducing-balance method used by lenders in the markets the tool names. Rates are yours to set; the tools ship with clearly-labelled example defaults, not official rates.
Tax
Figure
Source
US federal income tax brackets and standard deduction
Internal Revenue Service (IRS) annual revenue procedures. [cited]
US state sales-tax rates
The individual state Departments of Revenue. There is no single national sales-tax authority in the US — combined rates include local taxes and are the most changeable figures on this site. [governing]
UK income tax bands, personal allowance, VAT and Stamp Duty (SDLT) rates
HM Revenue & Customs (HMRC) and the UK Government’s published rate tables; Scotland’s income-tax bands follow the Scottish Government’s rates, and SDLT applies to England & Northern Ireland (Scotland’s LBTT and Wales’s LTT are separate systems, and the tool says so). [cited]
Australian income-tax rates and GST
Australian Taxation Office (ATO) resident rate tables. [cited]
Canadian federal and provincial tax, GST/HST rates
Canada Revenue Agency (CRA) published brackets and provincial rate tables. [cited]
EU VAT rates
The European Commission’s published member-state rate lists; the rate that applies is set by each member state. [governing]
ABN checksum
The Australian Business Register’s published ABN format and checksum rule — the validator checks format only; whether an ABN is active can only be confirmed on the official ABR Lookup. [cited]
Health
Figure
Source
Medicare Part B premiums and IRMAA tiers
Centers for Medicare & Medicaid Services (CMS) published premium and IRMAA tables. [cited] Figures for a future year are the Medicare Trustees’ projection and are labelled as a projection on the page (the 2027 Part B figure of $209.50/month is the current example). [cited]
ACA subsidy percentages and benchmarks
IRS revenue procedure for the stated year (applicable percentage table), with Federal Poverty Level figures from the U.S. Department of Health and Human Services (HHS) annual guidelines. [cited / governing]
BMI bands
The standard World Health Organization (WHO) adult BMI classification that the CDC also uses. [governing]
Calorie and BMR figures
No official source — published equation. The Mifflin-St Jeor equation, the peer-reviewed formula most commonly used by dietitians; activity multipliers are coaching conventions, and the pages say the results are estimates, not medical advice.
Sleep-cycle timing
No official source — convention model. 90-minute sleep cycles are a widely used planning convention; the duration guidance echoes the CDC’s published recommended sleep hours. [governing for durations only]
Ovulation and due-date figures
Clinical convention. Naegele’s rule and standard cycle maths, consistent with the dating approach described by the American College of Obstetricians and Gynecologists (ACOG). A professional body’s convention, not a regulator’s table — see the pregnancy note on the pages themselves.
Travel
Figure
Source
Live flight data
Live flight positions from the OpenSky Network API (the Flight Tracker displays third-party live data; it is only as current as that feed). [governing]
Time-zone offsets and DST rules
The IANA Time Zone Database — the standard reference every operating system uses. [governing]
Fuel-cost and trip-budget figures
No official source — estimate model. These tools multiply your own prices, distances and budgets; no authority publishes the inputs, so none is claimed.
Math & Education
Pure mathematics needs no source beyond the definitions themselves (LCM, GCF, percentage, GPA scales follow the standard 4.0 convention used by most US schools). Two exceptions, stated plainly: the SAT and LSAT score calculators are unofficial estimates — the College Board and LSAC publish the real scoring scales and do not endorse third-party estimators.
Family, Pets & Animals
Figure
Source
Due-date and pregnancy maths
Naegele’s rule / ACOG dating convention (see Health).
Baby first-year costs
No current official source — estimate model. Figures are US-average planning estimates, as the page itself states. (The USDA’s Cost of Raising a Child report was the standard reference but has not been updated since 2017; we do not present it as current.)
Dog and cat age conversion
Veterinary convention, not a biological constant: the dog conversion follows the size-based life-stage chart used in the American Veterinary Medical Association’s public guidance; the cat conversion follows widely used veterinary life-stage charts — a rule of thumb, as the tool itself says.
Dog chocolate toxicity thresholds
Published veterinary toxicology — the theobromine dose bands set out in the Merck Veterinary Manual. The calculator is a triage aid, never a substitute for a vet — in a real incident, call a vet or an animal poison line (such as ASPCA Animal Poison Control) first. [governing]
Chinese Gender Predictor
No source — folklore, offered as entertainment. The page itself already says the chart is legend, “not a verified document”. It makes no medical claim and we label it accordingly.
Home, Garden, Cars, Work & Cooking
Concrete bags, paint, materials: manufacturer yield and coverage tables (e.g. a standard 80 lb concrete bag yields ≈0.6 cu ft; paint covers ≈350 sq ft per gallon) — industry conventions printed by manufacturers, not regulators. Quantities are buying estimates; the tools add the waste allowances they state.
Car running costs: your inputs drive the result. Where a consumption figure is needed, the reference point is the U.S. EPA’s published ratings at fueleconomy.gov. Depreciation is a market model — no official source.
Work & career: pay conversions are arithmetic on your figures; the contractor-vs-employee tool’s tax side follows the same IRS/HMRC/ATO tables as the Tax section. Meeting-cost and similar tools are models with no external figures.
Cooking: turkey cooking times and safe temperatures follow USDA Food Safety and Inspection Service guidance [governing]; portion and scaling tools are culinary convention.
Utilities: unit conversions follow the SI definitions maintained by the Bureau International des Poids et Mesures (BIPM) under the Metre Convention — NIST is the US national metrology authority, not the SI’s keeper [governing]; the password generator favours length over complexity, the approach modern guidance recommends; QR codes follow the ISO/IEC 18004 standard.
PDF & image tools: these transform your files, not figures — there are no rates to source. The photo tools are the exception: the DS-160 tools and Passport Photo Maker are built to the U.S. Department of State’s published photo requirements (the DS-160 specification is the State Department’s own document; passport photo sizes additionally follow the ICAO Doc 9303 standard that passport specifications rest on). [governing]
Figures with no official source — the honest register
The following tools produce estimates from models, published equations or conventions, not official figures: Retirement Calculator (projections on your assumptions), Debt Payoff Calculator, Compound Interest Calculator, Calorie Calculator and BMR Calculator (Mifflin-St Jeor equation), Sleep Calculator, One Rep Max Calculator (published Epley/Brzycki formulas), Macro and Protein calculators (coaching guidelines), Baby Cost Calculator, Wedding Budget Calculator, Car Depreciation Calculator, Pet Insurance ROI Calculator, AI API Cost Calculator (vendor-published price lists — the vendors are the source, and prices change without notice), SAT and LSAT Score Calculators, Chinese Gender Predictor (folklore/entertainment). Each of these pages states its assumptions; none of them presents a model output as an official figure.
Last reviewed: [the real date this page’s content is published or materially revised — never an auto-generated “today”]. Questions or corrections: via the contact page — corrections go to the top of the list.