How Our Calculators Work

How to read our estimates

Pay Budget Debt calculators use the values you enter plus the formulas or assumptions described below. Results are intended for comparison and planning, not as loan offers, tax advice, investment guarantees or individualized financial advice.

Small differences in rounding, payment timing, fees, tax treatment, lender rules or market conditions can produce different real-world results.

Loan and mortgage payment formulas

Fixed-rate installment tools use a standard amortizing-payment formula. For a principal balance P, periodic rate r and number of payments n:

When the periodic interest rate is zero, principal is divided by the number of payments. The Auto Loan and Mortgage tools use this approach, with the purchase-specific costs entered in each calculator.

The Mortgage Refinance tool compares current and new principal-and-interest payments, includes the escrow inputs entered, and estimates break-even as closing costs divided by positive monthly savings. Its horizon comparison also considers the number of years you expect to keep the loan.

Affordability assumptions

The Home Affordability mode currently uses a 28% gross-income housing cap and a 36% total-debt cap. The Auto Affordability mode currently uses a 12% gross-income vehicle-cost cap and a 36% total-debt cap. The tool then works backward from the available payment to an estimated loan amount and purchase price.

These are built-in planning ratios, not lender underwriting rules. Home mode includes the insurance and HOA amounts entered but currently does not include property tax.

Debt payoff simulation

The Debt Payoff Simulator applies monthly interest to each entered balance, makes the modeled minimum payments, then directs available extra money according to the selected strategy. Snowball prioritizes smaller balances; avalanche prioritizes higher APRs. The model assumes the entered APRs and payment behavior remain consistent.

Compounding and savings formulas

The Money Compounding Calculator converts the annual rate into the selected periodic rate, grows the balance over time and applies recurring contributions according to their timing. The Savings Goal Calculator uses the same general future-value concepts to estimate time to a target or the recurring contribution required for a target horizon.

These calculations are mathematical projections. Investment returns, account rates, fees and taxes can change over time.

Budget and net worth calculations

The Budget Planner normalizes recurring expenses to a monthly view, totals expenses and compares them with the monthly income entered. Remaining savings capacity is monthly income minus modeled monthly expenses.

The Net Worth Calculator uses that direct relationship across the asset and debt categories entered.

Rent vs buy assumptions

The Rent vs Buy Calculator models rent growth, mortgage amortization, property tax, insurance and HOA, home appreciation, home equity and the opportunity cost of cash. In addition to user inputs, the current model uses these fixed assumptions:

• Maintenance: 1% of home value per year
• Buyer closing costs: 3% of home price
• Selling costs: 6% of home value at the end
• Return on modeled invested cash: 5% per year

These assumptions are intentionally transparent because actual costs and returns vary widely by market and household.

Retirement calculations

Accumulation mode grows current savings and recurring contributions using the return, compounding frequency and contribution-growth assumptions entered. It also reports an inflation-adjusted value by discounting the future nominal balance by the entered inflation rate.

Drawdown mode grows the remaining retirement balance by the assumed periodic return and subtracts the modeled spending gap between spending and other income. It can use either fixed nominal withdrawals or inflation-adjusted withdrawals.

The calculator does not predict market returns or calculate official Social Security benefits.

Paycheck tax assumptions

The Paycheck Calculator estimates annual gross pay from hourly or salary inputs, including modeled overtime and bonuses. It then subtracts estimated federal income tax, Social Security, Medicare and a simplified state income-tax amount.

For current federal withholding decisions, verify your situation with the IRS Tax Withholding Estimator or a qualified tax professional.

Accuracy and limitations

• Results depend entirely on the accuracy of the numbers entered.
• Rates, taxes, fees, laws and lender or employer rules can change.
• Many tools assume smooth rates or consistent payments for modeling purposes.
• Results may differ from lender disclosures, tax returns, investment statements or professional calculations.
• Use the calculators to test scenarios and ask better questions, not as a substitute for professional advice when the decision is material.