Calculation Methodology & Standards
At EverydayNumbers, accuracy and transparency are our highest engineering priorities. This document explains the arithmetic libraries, astronomical calendar rules, timezone algorithms, and physical conversion constants that power our calculators.
1. Arithmetic Precision & Floating-Point Safety
Standard computer programming languages represent numbers using IEEE-754 double-precision binary floating-point numbers. While fast for 3D graphics, binary fractions cannot represent common decimal numbers exactly (for instance, 0.1 + 0.2 = 0.30000000000000004).
To eliminate rounding drift in currency, tax, markup, and scientific ratios:
- Decimal-Safe Arithmetic: All financial and unit conversion calculations use arbitrary-precision decimal representations with 28+ digits of internal precision.
- Unrounded Intermediate Stages: Multi-step calculations never round partial results. Rounding occurs exclusively at final display time.
- Sensible Display Precision: Currency defaults to 2 decimal places; general numeric ratios retain up to 6 to 8 significant digits with trailing zeros cleanly trimmed.
2. Calendar Mathematics & Date Semantics
Calendar math is deceptively complex due to irregular month lengths (28 to 31 days), leap years, and civil daylight saving shifts. EverydayNumbers enforces rigorous semantic rules:
Date-Only Invariance
Calendar dates (e.g. October 4, 2026) are treated as pure civil calendar tuples (year, month, day) rather than UTC timestamps. This prevents day-boundary shifts caused by local timezone offsets.
Human Age & Anniversary Algorithm
Age is computed by advancing complete calendar years, then complete calendar months, then counting residual days. A person born on February 29 reaches their next civil birthday on February 28 during non-leap years.
Elapsed Days vs. Inclusive Days
By standard convention, the elapsed difference between Monday and Tuesday is 1 day. When "Include end date" is selected, both boundary days are counted (yielding 2 days).
Business Days & Holidays
Weekend schedules and observed federal holidays (such as holiday substitutions when a fixed date falls on Sunday) are evaluated algorithmically.
3. IANA Time Zone Database & Daylight Saving
Timezone conversions never use hardcoded fixed offsets (such as assuming London is always UTC+0 or New York is always UTC-5). Civil jurisdictions alter their UTC offsets twice a year for Daylight Saving Time (DST), and do so on different dates.
EverydayNumbers routes all timezone operations through standard IANA database identifiers (e.g. America/New_York, Europe/London, Asia/Tokyo). When converting a time on July 15 versus January 15, the calculator dynamically assesses the exact UTC offset applicable to that exact calendar instant.
4. Metrological Authorities & Physical Constants
All 10 unit converter engines on EverydayNumbers adhere to statutory definitions ratified by international metrology organizations:
Defines the seven SI base units (second, meter, kilogram, ampere, kelvin, mole, candela) in terms of invariant fundamental physical constants.
Authoritative US reference for conversion factors, significant figures, and proper usage of SI and non-SI units.
Harmonized binary prefixes (kibi, mebi, gibi, tebi, pebi) based on powers of 2 (1024) to resolve ambiguity with decimal SI metric prefixes (kilo, mega, giga, tera, peta).
Established exact international conversion standards: 1 international yard = 0.9144 meters exactly; 1 international avoirdupois pound = 0.45359237 kilograms exactly.
Defined 1 imperial gallon as exactly 4.54609 cubic decimeters (liters), superseding older definitions based on the volume of 10 pounds of distilled water.
Official Defined Conversion Multipliers
| Quantity | Unit | Symbol | Base Unit | Exact Multiplier to Base | Authority Reference |
|---|---|---|---|---|---|
| Length | International Inch | in | Meter (m) | 0.0254 | 1959 International Yard and Pound Agreement |
| Length | International Foot | ft | Meter (m) | 0.3048 | 1959 International Yard and Pound Agreement |
| Length | International Yard | yd | Meter (m) | 0.9144 | 1959 International Yard and Pound Agreement |
| Length | Statute Mile | mi | Meter (m) | 1609.344 | 1959 International Yard and Pound Agreement |
| Length | International Nautical Mile | NM | Meter (m) | 1852 | First International Extraordinary Hydrographic Conference (1929) |
| Mass | Avoirdupois Pound | lb | Kilogram (kg) | 0.45359237 | 1959 International Yard and Pound Agreement |
| Mass | Avoirdupois Ounce | oz | Kilogram (kg) | 0.028349523125 | 1959 International Yard and Pound Agreement |
| Mass | British Stone | st | Kilogram (kg) | 6.35029318 | 1959 International Yard and Pound Agreement |
| Mass | US Short Ton | ton | Kilogram (kg) | 907.18474 | NIST Handbook 44 |
| Mass | Metric Tonne | t | Kilogram (kg) | 1000 | BIPM SI Brochure |
5. Important Scope Limitations & Educational Notice
Not Professional Advice: The tools provided on EverydayNumbers are intended for general informational, educational, and everyday estimation purposes. They do not constitute certified accounting, professional tax advice, legal counsel, structural engineering, or medical diagnosis.
Taxes & Statutory Withholdings: Our Sales Tax and VAT calculators compute mathematical percentage additions and subtractions. They do not calculate multi-jurisdiction nexus rules, county surtaxes, specialized exemptions, or personal income tax brackets.
6. Corrections Policy & Bug Reporting
If you believe any calculation formula, conversion ratio, or calendar rule contains an error, we treat reports with urgent metrological scrutiny. Please contact our maintainers via our Contact & Feedback page including your exact input parameters, expected result, and citing authoritative reference standards.