Methodology
How WealthTrails calculators work: assumptions, formulas, data sources, and limitations explained.
Guiding Principles
Educational, not advisory
Outputs are illustrations to support learning and planning, not personalized recommendations.
Transparent assumptions
Inputs like expected return, inflation, and withdrawal rate drive outcomes. Changing them changes the result.
Verifiable sources
When we show market or rate data, treat it as a starting point. Always verify with primary sources.
Calculator Assumptions
Most tools let you adjust key assumptions. When those change, outputs change materially.
Expected Return
Annual nominal percentage used for growth projections.
Inflation
Translates between today's dollars and future spending power.
Tax Rate
Simplified effective rate to estimate gross vs net needs.
Withdrawal Rate
Planning parameter (e.g., 4%) to estimate portfolio size.
Note: These are simplified models. Real-life taxes, sequence-of-returns risk, fees, and behavioral factors can meaningfully change results.
Core Formulas
FIRE Number / Portfolio Target
Portfolio Target = Annual Spending ÷ Withdrawal Rate
Example: $60,000 annual spending with a 4% withdrawal rate = $1,500,000 target. Some tools also estimate gross spending needs by applying a tax adjustment.
Compound Growth
FV = PV × (1 + r)^n
Projection tools use compound growth with contributions over time. Outputs are sensitive to the return assumption and time horizon.
Data Sources & Updates
WealthTrails may display third-party financial data (ETF metrics, rates, benchmarks). Data can be delayed and is updated periodically.
- ETF metrics: Verify on the fund issuer site (prospectus/factsheet) or your brokerage.
- Rates & yields: Verify with the institution (bank/broker) or a primary market source.
- News: Content is sourced from publishers; read the original article for full context.
Limitations
Our tools are designed to be useful and understandable, not to model every real-world nuance. Common limitations include:
- Simplified tax treatment (effective rate, not marginal brackets)
- Simplified contribution timing (annual or monthly, not variable)
- Limited treatment of sequence-of-returns risk
- Fees and trading costs not always modeled
How to Cite WealthTrails
If you share a result, please link the specific tool page and include the assumptions used. That context is what makes the output meaningful and verifiable.
Example: "Based on WealthTrails FIRE Calculator with 7% return, 3% inflation, 4% withdrawal rate, and 12% effective tax."
Ready to explore?
Try our calculators and see these principles in action.