Methodology and assumptions

Where the numbers come from

The mortgage calculator uses the price, down payment, rate, term, and costs you enter. It does not fetch a credit report or a property record. A national mortgage average from FRED can be copied into the rate only when you choose “Use today’s average rate.” Until then, an example rate stays labeled as an example.

Displayed dollar amounts are rounded to the cent. The schedule is built from the same inputs, and the lifetime interest and payoff date are taken from that schedule.

Fixed payments and dates

A monthly fixed-rate payment uses the annual rate divided by 12 and a term measured in months. The first payment is in the start month you choose. Dates are calendar dates. The day is kept inside the month, so a short month does not roll into the next one.

A zero interest rate spreads the loan evenly across the number of payments. That path is only for testing. It is not a product the site is offering.

Extra payments and payment frequency

Extra principal is applied on the dates you set and is left out of the monthly housing payment. Biweekly drafts use half of the monthly principal and interest every 14 days, with interest on actual days over a 365-day year. Twice-monthly drafts use the 1st and the 15th.

Escrow and mortgage insurance on those accelerated schedules are modeled on the first draft of each calendar month. A servicer may not offer the same draft.

Mortgage insurance and program fees

Conventional PMI uses the annual rate you enter, on the original loan, while the model still treats it as required. Automatic termination is modeled at 78% of original value. Requested cancellation at 80% is modeled only for a primary residence when the loan is assumed to stay current. That is a model of the threshold, not a finding that a loan qualifies.

FHA, VA, and USDA fees use assumptions stored with the calculator and a review date shown beside them. They are not agency quotes. Jumbo loans do not add mortgage insurance unless you enter a rate for it. These tables need to be checked again before they are described as current.

Needs review before launch. Program fee tables and mortgage-insurance cancellation rules need a fresh check against the source documents before public launch.

Adjustable-rate scenarios and closing cash

An ARM path uses the product timing and caps you enter. The rate after the fixed period moves toward the scenario rate you typed, limited by the initial, periodic, and lifetime caps. The margin and index are recorded. They are not added to produce the rate.

Cash to close starts from the down payment and the costs you enter, then subtracts credits and earnest money. Financed upfront fees stay in the loan balance instead of being added to cash due a second time. Credits do not reduce principal. The result is not allowed to go below zero.

Home affordability and debt-to-income

The affordability calculator searches for a price whose estimated housing payment fits the scenario you select. Income is gross. A monthly override, when it is not zero, replaces the income built from the amounts and frequencies you enter. Additional income and a co-borrower are included only as annual amounts you type.

The housing budget is the lower of the housing-ratio cap and the room left under the total-obligation ratio after the debts you enter. Groceries and utilities are not added to that debt total. An optional household amount can lower only the comfortable budget. Cash to close can also cap the price when that constraint is on. The stored closing percentage is illustrative. It is not a closing disclosure, and a result is not an approval.

Needs review before launch. Debt-to-income limits used by agencies and lenders are not stored here as current quotes.

Refinance break-even

The refinance comparison uses the current balance, rate, and remaining term you enter, and a new loan built from the rate, term, costs, and purpose you enter. A simple break-even divides the cash financing cost by the monthly payment savings. It is left uncalculated when the new payment is not lower.

The economic comparison follows principal, interest, and mortgage insurance, plus the remaining balance, and it does not treat a new escrow deposit as money lost. Cash-out proceeds are money received. A lower payment is reported separately from total interest, because a longer term can reduce the payment and increase interest. The page does not calculate a tax deduction.

Needs review before launch. Tax treatment of points, credits, and cash-out is not modeled.

Auto loan amortization, trade equity, and sales tax

The auto loan calculator uses a fixed monthly schedule. Interest for a month is the unpaid balance times the APR you enter, divided by 12, and rounded half-up to the cent. The contractual payment is rounded the same way. The last payment clears the remaining principal. Extra principal is applied after the scheduled principal and only up to the balance that remains. Interest is not accrued by the day.

Trade equity is the allowance minus the payoff. Positive equity reduces the amount financed once and is not also added as cash down. Negative equity is either financed or paid in cash, and the result says which. Sales tax is illustrative: full-price mode taxes the vehicle price, and trade-credit mode subtracts the allowance before tax. A rebate can come off before tax or after tax. Title and registration stay outside the tax. No state is selected and no local rate is fetched.

Needs review before launch. Sales-tax rules differ by state. The two modes are illustrations, not a determination of tax due.

Interest, compounding, and what is not modeled

Where a loan calculator is published, interest is the monthly charge described above. The rental calculator uses that same principal-and-interest schedule and then subtracts rent, vacancy, and operating expenses you enter. The compound interest calculator is separate. It posts the annual rate you enter at a yearly, quarterly, monthly, or daily frequency, and it adds the contributions you enter. A 365-day year is used for daily posting, with no leap day. The mortgage payoff calculator uses that same monthly schedule and applies extra principal after the scheduled principal, capped at the remaining balance. The debt payoff calculator is separate. It charges one-twelfth of each annual rate you enter, rounded half-up to the cent, applies each minimum, then sends the extra payment either to the highest rate or to the smallest balance. A minimum from a balance that has already reached zero is added to the extra the next month. Taxes, insurance, and mortgage insurance are left out of that comparison. The retirement calculator uses the monthly compound schedule until the retirement age you enter. Contributions stop then. A withdrawal you enter is taken after interest each month and cannot exceed the balance. Social Security, taxes, and inflation are not calculated. The credit card payoff calculator charges one-twelfth of the APR you enter each month, applies either a fixed payment or the minimum rule you enter, and stops after 600 months if a payment never covers the interest. The student loan calculator reuses the loan amortization schedule for standard and extended plans, solves a simplified graduated schedule, and shows a rough income-based estimate from numbers you enter; it does not check eligibility or forgiveness. The 401(k) calculator deposits your contribution and any employer match monthly, caps your deferrals at the annual limit you enter, and compounds the balance at the return you enter. Vesting and taxes are not calculated.

None of the calculators fetch a live rate, a credit report, or a property record. Program fee tables carry a review date and are not current agency quotes. A lender or servicer can accrue interest, round, or collect fees differently from these models.