Editorial Policy & Methodology

Every calculator on Smart Kit Now starts from a published formula, not from an internal approximation. When a field already has an accepted standard, we implement that standard and name it on the page so you can check our work against the original source. A few concrete examples from the tools currently live on the site:

• Health & fitness. Basal metabolic rate uses the Mifflin-St Jeor equation (1990) rather than the older Harris-Benedict, because it was calibrated on a more representative population. Body fat uses the US Navy circumference method (neck, abdomen, and hip or chest). Body surface area offers Du Bois and Mosteller; one-rep-max offers Epley and Brzycki; heart-rate zones offer Karvonen and Tanaka; ideal weight shows Hamwi, Devine, and Miller side by side instead of quietly picking a winner. Pregnancy dating follows Naegele’s rule, and activity burn uses MET values from the Compendium of Physical Activities.
• Financial. Loan, mortgage, and amortization tools use the standard fixed-payment amortization formula, M = P · i(1 + i)ⁿ / ((1 + i)ⁿ − 1), with compounding stated explicitly. Tax and mileage tools reference published IRS figures for the relevant year.
• Construction. Brick and mortar quantities follow the Brick Industry Association’s Technical Notes on Brick Construction, including the waste allowances the notes recommend rather than a round number we invented. Concrete and rebar tools reference ACI 318.
• Electrical. Conductor sizing, ampacity, breaker selection, and load calculations reference the National Electrical Code tables by number — NEC 310.16 for ampacity, 240.6(A) for standard overcurrent device ratings, 220.12 for general lighting loads, 430.250 for motor full-load current — alongside Ohm’s law for the underlying arithmetic.
• Conversion, science, pets, and cooking. Unit factors come from NIST-published values; date and duration handling follows ISO 8601; pet feeding and body-condition tools reference AAHA and WSAVA guidance; food and nutrient figures come from USDA data.

Implementing a formula correctly is a separate problem from choosing the right one, so no calculator goes live on the strength of its code alone. Before a tool is published, its results are recomputed independently — by hand or in a spreadsheet, straight from the published formula — and compared against what the page returns. We check at least a typical case and the boundary cases: zero, negative, and out-of-range inputs, and the point where a result changes category (a BMI crossing 25, an ampacity crossing to the next conductor size). Tools that accept both metric and imperial input are checked in both, because unit conversion is where most calculator errors actually live.

We also publish the math instead of hiding it. Of the 732 calculator components in the codebase, 511 display the underlying formula on the page with each variable defined, and 496 include a step-by-step worked example you can follow to confirm the tool is doing what it claims. Bringing the remainder up to that standard is ongoing work, not a finished state, and it is the single largest item in our backlog.

We get things wrong. When that happens we want to hear about it quickly, and a reproducible math error jumps the queue ahead of every feature we had planned.

To report one, use our contact page or email contact@smartkitnow.com. The most useful report includes the page URL, the exact inputs you entered, the result you got, and the result you expected — ideally with the source you are comparing against. We reproduce the issue, recompute from the original formula, and if the error is confirmed we fix it and audit every other calculator that shares the same math, since one bad conversion factor usually touches several tools. Where a correction changes the numbers a page previously returned, we say so on the page rather than editing it silently.

Every result on this site is an informational estimate. It is not financial, investment, tax, medical, veterinary, legal, or engineering advice, and it is not a substitute for a qualified professional who knows your situation.

• Health formulas are population models with real error bars. Mifflin-St Jeor carries roughly a ±10–20% standard error, and circumference-based body fat estimates typically land within ±3–4%. Use them as a starting point, not a diagnosis.
• Financial results depend on assumptions we cannot verify — rates, fees, taxes, and terms your lender may apply differently. Confirm any figure that affects a real decision with the institution involved.
• Construction and electrical estimates are quantity and sizing aids. Permitted work must be designed and signed off against your local code by a licensed professional; our numbers do not replace that review.
• Pet tools are general guidance. Feeding amounts, weight targets, and anything resembling a dose belong with your veterinarian.

A disclaimer to this effect appears on every calculator page. It is there because we mean it, not to satisfy a checkbox.

Alongside the calculators we publish 16 long-form blog articles, 132 practical smart-tip guides, and answered questions on nearly every calculator page. All of it is written in-house by the Smart Kit Now editorial team — the same people who build and check the tools — and credited as such on every post.

Drafts are written by whoever implemented the relevant math, then reviewed by a second person against three tests: every factual claim traces to a named source, every number in a worked example recomputes correctly, and nothing in the piece gives advice we are not qualified to give. Where drafting tools assist with structure or phrasing, a person still recomputes every figure and verifies every citation before publication; nothing goes live unread. When a source is revised — a new IRS mileage rate, an updated NEC table, a revised feeding guideline — we update the affected pages rather than leaving stale figures in place.

Smart Kit Now is free to use and paid for by advertising. Advertisers have no input into which calculators we build, which formulas we choose, or what our results say. Ads are served through an ad network and are never presented as part of a calculator’s output. Where a page includes a recommended-resources block, commercial entries are marked as sponsored. If a commercial relationship ever conflicted with getting a number right, the number wins.

You can read more about who we are on our About page, or reach us any time at contact@smartkitnow.com.