1. Formula sourcing
Every tool begins with the standard, published formula for its domain: the annuity payment formula for amortising loans, EMI and mortgages, the compound interest formula with contribution annuity for savings and SIP projections, WHO adult categories for BMI, the Mifflin-St Jeor equation for calorie needs, the US Navy circumference method for body fat, and proleptic Gregorian calendar arithmetic for all date maths.
We publish the formula on the page in plain notation, define every variable, state the assumptions it embeds, and list the primary sources we checked it against in a "Sources & references" section. If a tool cannot model something — fees, rate resets, public holidays — we say so rather than hiding the gap.
2. Separation of logic and interface
Calculation logic lives in pure, dependency-free functions that are independent of the user interface. That separation means the maths can be tested directly, reviewed in isolation, and reused without a browser.
Each function validates its inputs and returns a human-readable error rather than silently returning a misleading number. Zero denominators, future birth dates, out-of-range rates and non-numeric entries are rejected explicitly.
3. Automated testing
The calculation layer is covered by an automated unit-test suite that runs before every release. Tests assert known-good results — a £15,000 loan at 7.9% over four years must produce a payment of £365.49; 22:15 to 06:40 must return 505 minutes; 1/2 + 2/3 must reduce to 7/6 — plus the error paths for invalid input.
A change that breaks an expected result fails the build before it can reach the site.
4. Writing and review
- Every guide is written and reviewed by the DailyCalc Editorial Team, credited with a revision date on each calculator page.
- Each guide is written for one specific tool. We do not spin a template across pages, and we do not pad with keyword repetition.
- Worked examples use realistic magnitudes and show every arithmetic step, and each example is re-computed with the live calculator before publishing.
- Limitations and common mistakes are mandatory sections, not optional ones.
- Claims that depend on jurisdiction (tax slabs, statutory interest, tipping norms) are labelled with their jurisdiction and linked to the official source.
5. Corrections
Reader reports are the fastest route to a fix. When an error is reported, we reproduce the inputs, re-derive the result from the published formula, and either explain why the original figure was correct or correct the tool, its guide and its worked example together.
Substantive corrections update the revision date shown on the page so you can see when the content last changed.
6. Advertising and independence
DailyCalc is free to use and is funded by display advertising served by Google AdSense. Google chooses which ads appear; we do not sell ad space directly, and advertisers have no contact with us about content.
Ads are visually separated from calculators and guides and are never placed inside a result. No advertiser, lender, insurer, retailer or clinic influences a formula, a default value, a worked example, or the order in which tools appear. We do not publish sponsored calculators, paid reviews or affiliate lending links; if that ever changes, the relationship will be disclosed prominently on the affected page.
Questions about this page
If anything here is unclear, or you need a specific confirmation in writing, email contact@dailycalc.store or use the contact page, and tell us which document and section you are asking about.