Debt Payoff and Transfer Scenario Calculator

A browser-based calculator for modeling credit card payoff timelines under minimum-payment, fixed-payment, and promotional balance transfer scenarios.

Release Status

Version: 1.0 (internal)

This is the first working version and has only been reviewed internally.

What Changed

This README now reflects the current app behavior, including:

  1. Interest rates entered as percentages (example: 28 means 28%).
  2. Configurable minimum-payment rules for both current and transfer cards.
  3. Fixed-payment validation with inline fixes.
  4. A guided promotional transfer modal with preflight credit-limit checks.
  5. Transfer cost comparison summary (original interest vs. new total cost).

How It Works

1) Current Situation Card

Enter:

  1. Current Balance
  2. Current Interest Rate (APR as a percent)
  3. Start Date

The calculator outputs:

  1. Pay Off Date
  2. Months Left (includes a years-and-months breakdown when large)
  3. Interest Paid

You can open Current Card Settings with the gear icon to set:

  1. Bank's Absolute Minimum
  2. Balance Divisor (Balance / X)

The minimum payment formula is:

minimum = min(balance + monthly_interest, max(balance / divisor + monthly_interest, absolute_min))

The summary row below the heading shows the active floor and divisor.

2) Fixed Payment Mode (Current Card)

Enable Use Fixed Payment to compare minimum payments vs. a constant payment amount.

Validation rules:

  1. Fixed payment must exceed first-month interest, or balance will not decrease.
  2. Fixed payment cannot be below the required estimated minimum payment.
  3. When below minimum, the UI offers a one-click Fix button.

When valid, the app shows a savings message (interest saved and months saved) relative to minimum-payment baseline.

3) Promotional Transfer Flow

Click Promotional Transfer to open a guided modal flow.

Preflight step:

  1. Ask whether transfer card balance is currently $0.
  2. Collect credit limit (or available credit) before continuing.

Transfer setup captures:

  1. Transfer amount
  2. New card credit limit
  3. Fee terms: minimum fee and percent fee
  4. Promo rate, promo months, and post-promo rate
  5. New card minimum rules: divisor and absolute minimum
  6. Optional Pay off evenly over promo period

The preview panel explains, before applying:

  1. Current balance reduction
  2. New card balance including transfer fee
  3. Expected monthly payment for the new card
  4. Whether fixed-payment budget can be reallocated
  5. Warnings for over-transfer and credit-limit exceedance

Applying transfer updates the scenario by:

  1. Reducing current card balance by transfer amount
  2. Creating transfer card balance as transfer amount + transfer fee
  3. Showing Transfer Scenario card
  4. Carrying over promo terms and transfer configuration

4) Transfer Scenario Card

Outputs include:

  1. New Card Balance (w/ fees)
  2. Payoff Date
  3. Months Left
  4. Transfer Fee Added
  5. Interest Paid

Transfer card settings (gear icon):

  1. Credit limit
  2. Balance divisor
  3. Absolute minimum

Optional transfer-card fixed payment:

  1. Can be enabled independently from current card.
  2. Validates that payment is high enough to avoid negative amortization.
  3. Warns when payment is too low to clear during promo period.

5) Cost Comparison Summary

When a transfer is active, the app shows:

  1. Original total interest (baseline before transfer)
  2. Current card interest remaining
  3. New card interest
  4. Transfer fee
  5. New total cost (current interest + new card interest + fee)
  6. Estimated savings (or extra cost if negative)

6) Schedule Table

The table is generated monthly and updates live as inputs change.

Columns per card:

  1. Date
  2. Previous Balance
  3. Interest
  4. Balance with Interest
  5. Payment

If both current and transfer scenarios are active, both schedules are shown side by side.

Assumptions and Limits

  1. Estimates assume no new purchases.
  2. Interest is modeled monthly using APR/12.
  3. Calculations cap at 360 months (30 years) for safety.
  4. Results are planning estimates, not exact issuer statement math.

Reset Behavior

Reset All returns values and settings to defaults, hides transfer scenario, and clears validation errors.

Saved Preferences

The calculator saves your inputs, settings, and applied transfer scenario in your browser's local storage so they can be restored when you return. This information remains on your device and is not sent to a server.

Select Reset All to clear the saved calculator data and return to the default values. You can also clear it through your browser's site-data controls.

Running the App

This project is static HTML/CSS/JS.

  1. Open index.html directly in a browser, or
  2. Serve the folder with any simple local web server.

Disclaimer

This tool is for education and estimation only. Always confirm terms, fees, and required minimum-payment rules with your card issuer agreement.