arcitools / v0.1

Methodology

Every calculator on arcitools.com is built and maintained as a small editorial product, not a one-off script. This page documents how we build a tool, where the underlying numbers come from, how often we refresh them, how we fact-check, and how we respond when something is wrong. The goal is to give you — and any third-party reviewer — a clear, verifiable picture of the editorial process behind the numbers you see.

How a tool gets built

A new tool starts as a problem we (or a reader) actually hit. The full build pass looks like this:

  1. Define the decision. Pin down the specific Filipino household or small-business decision the tool answers in one sentence — e.g. "Should I take the 8% optional tax or graduated rates?", "Will rooftop solar pay back in my Meralco bracket?"
  2. Research the underlying rules. Pull the relevant primary sources: the tax code, regulator schedules, manufacturer pricing, operator-published rates. List the constants and their citations before writing any code.
  3. Model the math. Write the calculation in code with every constant called out by name and source. No magic numbers; no opaque formulas.
  4. Pressure-test edge cases. Zeros, negatives, the boundary values where tax brackets jump, currency thresholds, very large inputs, very small inputs.
  5. Ship a draft UI with sensible PH defaults. Every input is editable; no hidden assumptions. The default fuel price, interest rate, dividend rate, or depreciation curve is the current PH market value — not a US import.
  6. Write the "How it works" explainer. A non-technical reader should be able to understand what the math does and why each input matters.
  7. Document sources. Every external data point links back to a primary source. Tools that depend on third-party aggregators name them inline.
  8. Cold-review. A pass with fresh eyes 24 hours later, focused on naming, defaults, edge cases, and whether the answer matches a hand-calculated check.
  9. Publish with a Last reviewed date.

Where the numbers come from

We rely on first-party Philippine sources wherever possible. The primary sources behind our tools include:

Where a third-party aggregator is used (for example, fuel-economy estimates for vehicles we can't independently measure), the aggregator is named on the tool page. We do not rely on undisclosed sources.

Refresh cadence

Each tool carries a Last reviewed date below the calculator. Cadence varies by how fast the underlying data moves:

Tools that haven't been reviewed within their expected window get flagged in our internal backlog and the Last reviewed date stays visible so you know to double-check before acting on the result.

Fact-checking process

Before a tool ships, every constant in the code is traced back to a primary-source URL and cross-checked against a second independent reference where one exists (e.g. comparing the BIR's published bracket against the actual statutory text of the TRAIN Law). Worked examples in the "How it works" or article version of the tool are hand-calculated to confirm the code matches the spec.

For tools with multiple correct interpretations (different ways to amortize fees, different assumptions about reinvestment, different rounding conventions), the page explicitly states which convention is used and why.

Corrections policy

Numbers go stale. Rates change. We make mistakes. If something looks off — a rate, a fee, a formula — flag it via the contact page with a source link or a public regulator page. The workflow is:

  1. Acknowledge receipt within 2 business days.
  2. Verify the correction against the cited source.
  3. If confirmed, patch the constant or formula, re-run tests, and ship within 1–3 business days.
  4. Bump the Last reviewed date on the affected tool.
  5. Add a one-line changelog note for material corrections (anything that changes a result by more than a rounding amount).

We do not silently change numbers. Material updates are dated and noted.

Editorial independence

arcitools makes money from Google AdSense display ads and partner / referral links on tool pages where a relevant partner exists (credit cards, insurance, brokers, etc.). Every partner link is labeled Partner / issuer link below the button. We do not accept paid placement inside calculator math itself — defaults, rankings, and recommendations are independent of whether a partner pays a referral. We do not write sponsored articles, accept paid "thought leadership" placements, or take guest-post pitches built on backlink swaps.

The full source code, including every calculation and every constant, is public on GitHub. If you want to verify a formula or argue with a default, the math is right there.

Limits of the tools

Our calculators are informational. They are not financial, legal, tax, or professional advice. Results depend on the values you enter and on assumptions (inflation, dividend persistence, depreciation curves) that may not match real-world conditions for your specific case. For decisions with material consequences — a property purchase, a tax election, a large insurance plan — verify the numbers independently or consult a licensed professional before acting.

Questions about methodology, suggestions for new sources, or corrections — see the contact page.