Financial Calculator Methodology

Last updated: August 5, 2026

How Our Calculators Work

Every calculator on DolWise uses standard, publicly documented financial formulas. All calculations run entirely in your browser using JavaScript — we do not send your data to any server. This page explains the formulas, assumptions, and limitations behind each tool.

Mortgage Payment Calculator

Formula: Standard U.S. mortgage amortization — M = P × [r(1+r)^n] ÷ [(1+r)^n − 1] where M = monthly principal & interest, P = loan principal, r = monthly interest rate (annual rate ÷ 12), n = total payments (term in years × 12).

What it includes: Principal, interest, property taxes, and homeowners insurance (PITI). Property tax and insurance are divided by 12 and added to the monthly P&I payment.

What it does NOT include: Private Mortgage Insurance (PMI), HOA fees, closing costs, or lender fees. If your down payment is under 20%, budget 0.5%–1.5% of the loan amount per year for PMI.

Source: CFPB — Owning a Home: Loan Options. Interest rates are illustrative.

Loan Payoff Calculator

Method: Month-by-month amortization simulation. Each month, interest is calculated on the remaining balance, then the payment (minus interest) goes toward principal. The simulation runs until the balance reaches zero or 1,200 months (100 years).

Assumptions: Fixed interest rate, fixed monthly payment, no prepayment penalties, no skipped payments, no fees.

Source: Standard amortization methodology. See also: CFPB — Prepayment Penalties.

Debt-to-Income (DTI) Ratio Calculator

Formula: Front-end DTI = Monthly housing payment ÷ Gross monthly income. Back-end DTI = Total monthly debt payments ÷ Gross monthly income.

Thresholds: Conventional mortgage guidelines: ≤36% recommended for total DTI; FHA loans may allow up to 43% with compensating factors; some programs go higher. Thresholds are general guidelines, not guaranteed approval criteria.

Source: CFPB — What is a debt-to-income ratio?

Credit Card Payoff Calculator

Method: Month-by-month balance simulation. Each month, interest is calculated (APR ÷ 12 × remaining balance), then the payment (minus interest) reduces the balance. The simulation runs until the balance is paid off or 1,200 months.

Assumptions: No new charges, no annual fees, no balance transfer fees, fixed APR.

Source: CFPB — How credit card interest is calculated.

Hourly to Salary Calculator

Formula: Estimated annual gross pay = (Hourly rate × Regular hours/week × Weeks worked/year) + (Hourly rate × Overtime multiplier × Overtime hours/week × Weeks worked/year).

What it does NOT include: Taxes, Social Security, Medicare, benefits, bonuses, commissions, or deductions. This is gross pay only, not take-home pay.

Source: U.S. Department of Labor — Overtime Pay.

Savings Goal Calculator

Method: Month-by-month compound interest simulation: balance = balance × (1 + monthly rate) + monthly contribution. Runs until the goal is reached or 1,200 months.

Assumptions: Constant annual return rate, no taxes on interest, no withdrawals, no fees. Real-world returns fluctuate; this is a projection tool, not a guarantee.

Source: Standard compound interest formula. SEC Investor.gov — Compound Interest Calculator.

Testing Procedure

All calculators are tested with the following input vectors before publication:

Limitations

All calculators on DolWise provide estimates for informational purposes only. They do not constitute financial, tax, legal, or investment advice. Results should not be relied upon for financial decision-making without consulting a qualified professional who understands your specific circumstances.

Corrections

If you find an error in any calculator, please report it through our Contact page. We review and correct verified errors promptly.