Our Accuracy Commitment

Every tool on Allio Tools is built against a published standard, peer-reviewed formula, or widely adopted industry specification. We document the source of each formula here so you can independently verify results. If you find a discrepancy, please report it — we correct formula errors within 48 hours of verification.

All calculations use JavaScript's 64-bit IEEE 754 floating-point arithmetic, which provides 15–17 significant decimal digits of precision — identical to Microsoft Excel, Google Sheets, and Python's float type. Where intermediate rounding is required, we use round-half-up (the standard convention in finance and medicine).

Financial Calculators

Mortgage Calculator

Uses the standard fixed-rate annuity formula: M = P[r(1+r)ⁿ] / [(1+r)ⁿ−1], where P = principal, r = monthly interest rate (annual ÷ 12), n = number of payments. This formula is specified in the U.S. CFPB mortgage regulations and produces identical results to Excel's PMT() function.

Loan Calculator

Uses the same annuity formula as the Mortgage Calculator. Amortization schedules are computed iteratively: each month's interest = remaining balance × monthly rate; principal = payment − interest; new balance = old balance − principal paid.

Compound Interest Calculator

Formula: A = P(1 + r/n)^(nt), where P = principal, r = annual interest rate (decimal), n = compounding periods per year, t = time in years. For continuous compounding, A = Pe^(rt). Both formulas follow NIST Handbook 29 and standard actuarial practice.

Investment Return Calculator

Total return uses: Return% = ((Ending Value − Starting Value) / Starting Value) × 100. CAGR uses: CAGR = (Ending / Starting)^(1/years) − 1. These are the standard definitions used by CFA Institute and the SEC in performance reporting.

Currency Converter

Exchange rates are fetched in real time from the Frankfurter API, which sources data from the European Central Bank (ECB). ECB rates are published on each business day at 4 PM CET.

Health Calculators

BMI Calculator

Formula: BMI = weight(kg) / height(m)². Imperial input is converted (lbs × 0.453592 = kg; inches × 0.0254 = m) before calculation. BMI classification thresholds (Underweight <18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese ≥30) follow WHO Technical Report Series 894 (2000) and are consistent with CDC guidelines.

TDEE Calculator

Resting Metabolic Rate (RMR) uses the Mifflin–St Jeor equation (Mifflin et al., 1990, Journal of the American Dietetic Association), which is recommended by the Academy of Nutrition and Dietetics as the most accurate predictive equation for the general population:

  • Men: RMR = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) + 5
  • Women: RMR = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) − 161

Activity multipliers follow the Katch & McArdle (1996) activity factor system: Sedentary ×1.2, Light ×1.375, Moderate ×1.55, Active ×1.725, Very Active ×1.9.

Body Fat Calculator

Uses the U.S. Navy circumference method (Hodgdon & Beckett, 1984), which estimates body fat from neck, waist, and hip measurements. This method is within 3–4% of DEXA scan measurements for most adults and is the method used by the U.S. military for fitness assessments.

Ideal Weight Calculator

Provides results from four established formulas: Robinson (1983), Miller (1983), Hamwi (1964), and Devine (1974). Each was developed for clinical settings and targets 5'5" (165cm) as the baseline. Results are shown together so users can understand the range rather than relying on a single estimate.

Calorie Calculator

Uses TDEE as the base. Deficit/surplus targets follow the principle that 1 lb (0.45 kg) of body fat ≈ 3,500 kcal, consistent with NIH guidance. Note: this "3,500 kcal rule" is an approximation; real-world results vary due to adaptive thermogenesis. Our tool presents it as an estimate, not a precise prediction.

Pregnancy Due Date Calculator

Naegele's Rule (standard clinical method): EDD = LMP + 280 days (40 weeks). LMP = first day of last menstrual period. This method is used by ACOG (American College of Obstetricians and Gynecologists) and produces dates consistent with ultrasound-based dating within ±5 days for most pregnancies.

Developer Tools

URL Encoder / Decoder

Follows RFC 3986 (Uniform Resource Identifier). Uses JavaScript's encodeURIComponent() and decodeURIComponent(), which encode per RFC 3986 §2.1 using percent-encoding for all characters except unreserved characters (A–Z, a–z, 0–9, -._~).

Base64 Encoder / Decoder

Follows RFC 4648 (Base64 Data Encodings). Uses the standard alphabet (A–Z, a–z, 0–9, +, /, =). The URL-safe variant (RFC 4648 §5) substitutes + with − and / with _.

Hash Generator

Uses the browser's native SubtleCrypto.digest() API (part of the Web Cryptography API, W3C Recommendation). Supports SHA-1 (not recommended for security), SHA-256, SHA-384, and SHA-512 as specified in FIPS PUB 180-4.

UUID Generator

Generates UUIDs following RFC 4122 §4.4 (Version 4, random). Uses crypto.randomUUID() where available (browsers with Web Cryptography API support), falling back to crypto.getRandomValues() to fill a 16-byte array. Both methods are cryptographically secure.

Regex Tester

Uses the browser's native ECMAScript regular expression engine (V8 in Chrome/Edge, SpiderMonkey in Firefox, JavaScriptCore in Safari). Behaviour follows the ECMAScript 2023 specification (ECMA-262), including support for named capture groups, lookahead/lookbehind, and the u (Unicode) and d (indices) flags.

JWT Decoder

Decodes the header and payload of a JSON Web Token using standard Base64URL decoding (RFC 7519). The tool does not validate the signature (which requires the secret key). Output shows the decoded claims exactly as embedded in the token.

Limitations and Disclaimers

All calculators produce estimates. Population-based formulas (BMI, TDEE, body fat) can differ from measured values by 10–25% for individuals with atypical body composition, chronic conditions, or unusual metabolic profiles. Financial calculations assume fixed rates and do not account for variable-rate changes, tax implications, or fees unless explicitly stated.

Health results are for informational purposes only and do not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before making health or dietary decisions.

Financial results are for illustrative purposes only. Always verify significant financial decisions with a qualified financial advisor.

Reporting Errors

If you believe a formula is incorrectly implemented or references an outdated standard, please contact us with the tool name, the input values you used, the result you received, and the result you expected (with a source citation if possible). We investigate every report and correct verified errors within 48 hours.