Editorial standards

Methodology & sources

BorderTally is a calculator site, so the value of each page is the calculation plus the explanation around it: where the rule came from, what the formula includes, and where the estimate stops being reliable.

Build standards

How we build calculator pages

We separate formulas from copy

Calculator engines live as pure functions and are covered by tests. Page copy explains the result, but the numbers come from the same rule tables used by the UI.

We show source age

Rule-backed tools carry a checked date, a data-as-of or rules-as-of value, and source links where the underlying authority publishes the rule.

We avoid false precision

When a real-world answer depends on a local tariff code, exact address, university evaluator, visa status, or travel date, the calculator returns a planning estimate and explains the missing detail.

We keep personal inputs local

The public calculators run in the browser. We do not ask for an account to use them, and ordinary calculator inputs are not uploaded to our servers.

Source notes

Tool-by-tool source notes

Tool Source basis Known limits
Import duty & landed cost Customs and tax authority pages linked from each destination rule table. Uses simplified category buckets. Final charges depend on the exact commodity code, origin proof, customs reliefs, courier process, and rule changes.
Schengen 90/180 calculator European Commission Schengen visa guidance and the short-stay rule linked on the tool page. Counts calendar days under the rolling window, but cannot decide your border eligibility, residence status, visa type, or officer discretion.
VAT & sales-tax calculator National tax authority pages for VAT rates and state-level sales-tax references for US states. VAT category eligibility and local US sales taxes can change the final answer. US state rates are a floor, not the combined delivery-address rate.
GPA & grade converter Documented conversion bands and country-specific grading references where available. Admissions offices and credential evaluators can use their own policy, so the result is a planning range rather than an official evaluation.
Cost of living & take-home pay Indicative city index snapshots and widely known tax bands marked with data-as-of labels. City averages hide neighbourhood rent, household size, benefits, filing status, local tax, healthcare, childcare, and exchange-rate movement.
Travel budget planner Destination preset snapshots reviewed by month and editable by the user. Presets are not live quotes. Season, availability, exchange rates, route choice, and travel style can change the real budget.
Unit, currency, and date converters Deterministic unit definitions plus a dated FX snapshot for exchange-rate examples. FX values are indicative unless marked live; banks, cards, and exchanges apply their own spreads and fees.

Workflow

Review process

  1. Find the official or defensible source A calculator page should link to the source authority or explain why the value is an indicative planning snapshot.
  2. Encode the rule in data Thresholds, rates, and labels go into versioned data files so the same source powers the UI, generated pages, and tests.
  3. Test the calculation path Core engines have node:test coverage for representative calculations and edge cases before a tool is marked live.
  4. Label limitations on the page Each tool explains what it includes, what it excludes, and when a visitor should confirm with an official source.

Corrections

Found a stale rule?

Send the page URL, the value you believe is wrong, the expected value, and the source. We update source-backed corrections before adding new landing pages.

Email a correction

FAQ

Methodology FAQ

Can I rely on a BorderTally result as professional advice?

No. BorderTally provides planning estimates only. Confirm tax, customs, immigration, academic, and financial decisions with the relevant authority or a qualified adviser.

How do I report a stale rate or rule?

Use the contact page and include the calculator URL, the wrong value, and the official source you are referencing. We prioritize corrections that include source links.

Why do some pages say a rate is broad or needs verification?

Some real-world rules depend on exact categories that are too granular for a simple consumer calculator. We mark those cases instead of pretending the result is exact.