Methodology
This page explains exactly how the calculators on LoanSHelper.ai produce their numbers: the formulas, the data behind the default rates, how worked examples and simulated scenarios are labelled, and what the tools leave out. If anything here disagrees with what a page shows, tell us — the page gets corrected and the change noted.
What the tools compute
- Monthly payment uses the standard amortization formula, M = P × r(1+r)n / ((1+r)n − 1), where P is the loan amount, r is the monthly rate (annual rate ÷ 12) and n is the number of monthly payments.
- APR is solved numerically: we find the rate at which the net amount you actually receive (loan minus lender fees and points) produces the contractual monthly payment — the same approach a lender's disclosure uses.
- DTI shows a front-end ratio (housing payment ÷ gross income) and a back-end ratio (all monthly debts ÷ gross income). The maximum-loan estimate uses a 43% back-end DTI and assumes roughly 25% of the housing payment goes to taxes and insurance.
- Affordability figures use the 28/36 guideline alongside the 43% back-end limit most conventional lenders apply.
- Break-even on a refinance or an offer comparison is closing costs ÷ monthly saving, in months.
Where the default rates come from
Default mortgage rates are the Freddie Mac Primary Mortgage Market Survey (PMMS) weekly averages for the 30-year and 15-year fixed-rate mortgage. Freddie Mac publishes the survey every Thursday; we update the site's rate file the same day, and every page that pre-fills a rate shows the survey week and date next to the field. The Rate Watch page keeps the weekly series, with the change versus the previous week and versus a year ago.
When the rate data fails to load
If the weekly rate file cannot be loaded, the Rate Watch widget says so — "Rate data temporarily unavailable" — and shows the date of the last successful update instead of a number. On the calculators, a pre-filled rate that could not be refreshed is cleared rather than left on screen, and a note next to the field tells you to enter your own rate. No page presents a stale figure as the current rate.
Worked examples
Every calculator page carries a labelled "Representative example" with round-number inputs. Where an example rate is the Freddie Mac weekly average, the example says so and gives the week. An example is an illustration of the arithmetic — never a quote, an offer, or a prediction of the rate any lender will give you. Your rate depends on your credit score, down payment, loan type, property and lender.
Simulated scenarios
The Rate Shock calculator's +0.25 / +0.5 / +0.75 / +1 point scenarios, and any similar what-if figures on this site, are hypothetical illustrations of what a payment would be at a different rate. They are not forecasts, and no page presents them as expected future rates.
What the tools do not model
- Taxes, insurance and HOA dues enter the totals only at the amounts you type in; the tools do not look them up.
- PMI is estimated at 0.75% of the loan per year when the down payment is under 20%. Real PMI pricing varies by credit score, insurer and loan structure.
- Credit-score pricing adjustments (LLPAs), lender overlays, state-specific taxes and fees, and discount-point strategies beyond the inputs shown are not modelled.
- Nothing here is an approval, a quote or financial advice. LoanSHelper.ai is not a lender, broker or financial advisor.
Sources and verification
Rates: Freddie Mac PMMS. Policy rates: Federal Reserve FOMC statements. Program rules: HUD/FHA handbooks, the Department of Veterans Affairs, Fannie Mae and Freddie Mac selling guides, and the Consumer Financial Protection Bureau. Figures in guides carry the date they were checked; if a figure is wrong or out of date we correct the page and note the change.
Who runs this site
LoanSHelper.ai is operated by Frontier Oak Property Holdings LLC. See About for the full picture — who we are, the other sites we run, and how this site makes money.