The Logic Behind the Tool

Here is the logic breakdown:

1. The Data Model (Cost of Living Indices): The tool relies on a central database (cityData) where every city is assigned a set of numerical indices.
   • National Average = 100: An index of 100 represents the US national average.
   • Indices Used:
   • Total Index: The weighted average of all costs.
   • Housing: Weighted at ~35% of a senior's budget.
   • Healthcare: Weighted higher for seniors (~15%) than standard calculators.
   • Groceries/Utilities: Weighted at ~25% combined.
   • Example: If NYC has a Total Index of 180, it is 80% more expensive than the national average. If Tampa has a 98, it is 2% cheaper than the national average.
2. The Core Income Formula: This is the "Ramsey-style" logic. It answers: “If I make $75k in DC, what do I need in Tampa?”
   Calculate the Multiplier:
   Multiplier = Destination Total Index / Current Total Index
   Example (DC to Tampa): 98 ÷ 145 = 0.675

   Calculate Needed Income:
   Needed Income = Current Income × Multiplier
   Example: $75,000 × 0.675 = $50,625

   Calculate Percentage Difference:
   (Destination Total Index − Current Total Index) / Current Total Index × 100
3. Category Breakdown Logic: To show the user why the number changed, the tool calculates the relative difference for specific life categories.
   (To Category Index − From Category Index) / From Category Index × 100

   This results in the “Housing is 45% lower” or “Healthcare is 10% higher” statistics shown in the progress bars.

4. Qualitative Logic (The "Verdicts"): The tool doesn't just show numbers; it uses "If/Then" logic to generate professional advice for seniors:
   • Housing Logic: If the destination housing index is lower, the logic triggers a message about “Unlocking Home Equity.” If higher, it warns about the need to “Downsize.”
   • Healthcare Logic: If the new city’s healthcare index is higher, the tool prompts the user to check their “Medicare Supplement networks.”
   • Tax Logic: If the destination is a no-income-tax state (like Florida), it highlights the “Immediate Raise” the senior gets on their 401k/Pension draws.
5. Replication Checklist: If you need to rebuild this from scratch, ensure you have:
   • A Lookup Table: A dictionary/object containing the indices for your target cities.
   • The Multiplier Engine: A function that takes (income, fromIndex, toIndex).
   • Comparison Labels: Logic to determine if the result is “Higher” or “Lower” to apply the correct color.
   • UI Feedback: A scroll-to-result trigger so the user knows the calculation is finished.