1. Formula sourcing
Every tool begins with the standard, published formula for its domain: the annuity payment formula for amortising loans and EMI, the compound interest formula with contribution annuity for savings projections, WHO adult categories for BMI, and proleptic Gregorian calendar arithmetic for all date maths.
We publish the formula on the page in plain notation, define every variable, and state the assumptions it embeds. 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 TypeScript 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 throws 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 on every build. Tests assert known-good results — a £15,000 loan at 7.9% over four years must produce a payment of about £365.42; 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 standards
- 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, including a reverse check where one exists.
- 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.
5. Corrections
Reader reports are the fastest route to a fix. When an error is reported through the contact page, 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. Independence
DailyCalc is free to use and carries no advertising, no sponsored calculators, no affiliate lending links and no paid placements. No lender, insurer, retailer or clinic influences a formula, a default value, or the order in which tools appear.
If that ever changes, any commercial relationship will be disclosed prominently on the affected page before you use it.
Questions about this page
If anything here is unclear, or you need a specific confirmation in writing, write to us through the contact page and tell us which document and section you are asking about.