How the tools work

Calculator Methodology

Sunset Guardian calculators are designed to make financial tradeoffs easier to inspect. This page explains the shared methods, privacy choices, and limitations behind the results.

A calculator can organize assumptions and perform consistent arithmetic. It cannot know every account rule, tax consequence, fee, future rate, or household priority.

Each result should be read together with the assumptions shown on the calculator page. When a lender, card issuer, account statement, plan document, tax rule, or contract differs from the calculator, the governing document controls.

Calculations in the browser

Sunset Guardian calculator code performs the calculations in the visitor's browser using JavaScript. The calculator pages do not submit entered financial values to a Sunset Guardian form or calculation server.

This includes values such as balances, payments, rates, contributions, time periods, and calculated results. Reloading or leaving a page generally clears the active calculation unless the browser itself retains a field value.

No account is required for the current calculators. Future site features may use accounts or saved settings, but the calculators described on this page currently run without a Sunset Guardian login.

Privacy-conscious analytics

The site uses standard page analytics to understand whether pages are visited and whether the site performs properly. It also uses two limited calculator events:

  • calculator_used records that a visitor made a genuine change to a calculator field.
  • related_guide_clicked records that a visitor followed a calculator's related-guide link.

Those custom events include a fixed calculator identifier, such as mortgage_extra_payment. They do not include entered balances, interest rates, payments, income, savings, results, or free-text values.

Standard analytics may still collect page and technical information as described in the Privacy Policy.

Shared calculation assumptions

Calculator-specific assumptions appear on each tool. Unless the page states otherwise, the tools commonly use the following approach:

  • Rates remain fixed for the period being modeled.
  • Payments or contributions occur at regular intervals.
  • Entered amounts are applied in the order explained on the calculator page.
  • No missed payments, late charges, withdrawals, or new transactions occur unless a field specifically models them.
  • Monthly calculations use the annual rate divided by 12 unless another method is stated.
  • A payoff simulation ends when the remaining balance is effectively zero after allowing for very small calculation tolerances.

Some tools use future-value formulas. Others simulate one month at a time because rates, payments, fees, or promotional periods change during the comparison.

Precision and rounding

Calculations generally retain more precision than the page displays. Dollar results may be rounded to whole dollars for readability, while payment amounts may display cents.

A displayed total may therefore differ slightly from the sum of separately rounded values. Lenders and financial institutions may also use daily balances, different posting dates, statement-cycle rules, or their own rounding procedures.

A difference of a few cents or one displayed payoff month can result from rounding and payment timing. A large difference usually means that an assumption, fee, rate, or payment rule needs closer review.

Dates and payoff timing

When a calculator displays a payoff date, it estimates a month and year by adding the modeled number of months to the current month. It does not predict the exact statement date or final-payment day.

Actual timing can change because of payment posting, partial months, daily interest, weekends, holidays, grace periods, billing cycles, and institution-specific processing.

Duration comparisons are usually more reliable than treating the displayed month as an exact contractual payoff date.

Fees, taxes, and account rules

A calculator includes a fee or tax only when the page provides a field or clearly states an assumption for it. Common exclusions can include:

  • Annual account fees
  • Late charges and returned-payment fees
  • Escrow, property taxes, and insurance
  • Prepayment penalties
  • Tax deductions, credits, and filing interactions
  • Issuer-specific payment-allocation rules
  • Investment taxes and changing future returns
  • Promotional terms lost after a missed payment

Review the tool's explanation and the actual financial agreement before relying on a result.

Sources and review

Companion guides favor primary and authoritative sources when practical, including government agencies, regulators, official program documentation, and financial institutions responsible for the relevant rules.

Calculator logic is tested with known examples, boundary values, and independent calculations before publication. Changes are checked for JavaScript errors, invalid results, and unexpected values such as NaN or Infinity.

A calculator may still contain an error or may not represent an unusual product correctly. Material corrections should update the calculation, explanation, or companion guide rather than being hidden behind a changed example.

Using the results

Use a calculator to compare scenarios, identify the assumptions driving a result, and prepare better questions for a lender, adviser, tax professional, plan administrator, or other qualified professional.

Before acting on a large financial decision:

  1. Enter values from the current statement or official offer.
  2. Change one assumption at a time.
  3. Review the calculator's limitations and companion guide.
  4. Compare the result with the institution's own figures or governing documents.
  5. Preserve enough cash for foreseeable obligations and uncertainty.

Review the Financial Disclaimer for the site's broader educational-use limitations.

Focus on the assumption that changes the decision, then confirm it before committing money.