Are you actually ready to buy?

What this site is for

Ground Figures is a set of mortgage calculators with the reasoning written out next to them. Most mortgage tools give you a number and stop. The number is the easy part — what usually goes wrong is that the assumptions behind it were never stated, so a borrower plans around a figure that quietly assumed a property tax rate, an insurance premium, or a mortgage insurance cost that doesn't match their situation.

Every tool here shows what it assumed and lets you replace it. Every explainer says where a guideline is a hard program requirement and where it's a rule of thumb that underwriting weighs against everything else in your file. That distinction is most of the difference between advice that survives contact with an underwriter and advice that doesn't.

How every comparison on this site is scored

Almost every mortgage decision gets presented as a payment. Which is convenient, because the payment is the number a lender can quote you in ten seconds — and misleading, because it leaves out the two things that actually determine what an option cost you: the cash you handed over at closing, and the balance you still owe when you walk away.

So every comparison here is scored the same way, and the formula is written on the page rather than buried in a footnote.

That third term is the one that gets dropped, and dropping it reverses answers. Take a $450,000 purchase with 20% down — a $360,000 loan, $90,000 at the table — held seven years, comparing a 30-year at 6.75% against a 15-year at 6.05%:

Principal & interest only. Taxes, insurance, and mortgage insurance are identical across both and cancel out of the comparison.

On payment alone the 30-year wins by $713 a month, and it isn't close. On total cost the 15-year is ahead by $35,491 over the same seven years. Nothing was saved by the lower payment; it was deferred. The 30-year borrower built $33,165 of equity in that window. The 15-year borrower built $128,520.

This is not an argument for 15-year loans. The 30-year payment is $713 lower every month and that money is real — it covers a daycare bill, it funds a 401(k) match, it absorbs a job loss. Plenty of borrowers should take the 30-year for exactly those reasons. The point is narrower: a payment comparison told you the wrong thing, and it told you confidently. If you're going to choose the higher lifetime cost, choose it knowing the number, not because the only figure anyone quoted you was the monthly one.

The same correction applies anywhere cash and principal move independently — rent versus buy, refinancing, rate buydowns, seller concessions. In rent-vs-buy there's a fourth term most calculators also omit: what the down payment would have earned invested. Leaving it out systematically favors buying, so it's included here by default. The full accounting is on the methodology page.

Start where you actually are

If you're early and figuring out whether the numbers work at all, the affordability calculator and DTI calculator answer the two questions lenders ask first. If you're saving toward a purchase, the down payment savings calculator handles the timeline — including the part where your target moves while you chase it.

If you have a specific house in mind, the payment calculator gives the full PITI breakdown with an amortization schedule, and the scenario pages work through common price and down payment combinations end to end. If you already own, the refinance, extra payment, and PMI removal tools cover the decisions that come up after closing.

New terminology is handled in the glossary, and the formulas and assumptions behind every tool are documented in how we calculate these numbers.

Written by someone who originates loans

This site is built and written by a licensed Mortgage Loan Officer who is also a software engineer. That combination is the reason the tools model amortization and program rules directly rather than approximating them, and the reason the writing spends time on the places where published guidance and actual underwriting practice diverge.

Ground Figures doesn't take loan applications, doesn't sell leads, and isn't compensated by lenders. Nothing here is a loan offer. It's the math, with the assumptions visible.

What changed in 2026, and who it affects

Mortgage rules move more than most buyers expect, and the changes rarely arrive with an announcement that reaches borrowers. Four shifts this year are already reshaping deals in progress.

Condo financing got materially harder in August

As of August 3, the streamlined Limited Review pathway was eliminated for buildings with more than 10 units, and the minimum HOA reserve allocation rose from 10% to 15% of annual assessment income. The rules key off your loan application date rather than your contract date, which is catching buyers who went under contract in July. Expect two to four additional weeks on the closing timeline, and check the building before writing the offer — the reserve calculator screens it in about ten seconds, and the full guide covers what to do if a building fails.

Escrow shortages stopped being unusual

Property tax reassessments and homeowners insurance premiums have both climbed faster than servicers' prior-year estimates anticipated. The result is a wave of annual escrow analyses landing with shortages attached, and payments rising on loans where the rate never changed. The part that surprises people: your payment doesn't just rise by the shortage divided by twelve, it rises by that plus the increase in the ongoing monthly collection. Run the numbers here or read how escrow accounts actually work.

Student loan repayment was restructured

The end of the SAVE plan and the arrival of the Repayment Assistance Plan changed monthly obligations for millions of borrowers — which flows directly into mortgage qualifying, since student loan payments count toward debt-to-income. RAP's income tiers create cliffs where a modest raise produces a disproportionate payment increase. If you're planning to buy, the interaction is worth modeling before you apply: RAP calculator, where the tier cliffs fall, and what to do now that SAVE ended.

The 50-year mortgage conversation

Proposals to extend loan terms as an affordability fix resurface whenever payments outpace incomes. The arithmetic is less flattering than the headline: a longer term lowers the monthly payment modestly while increasing lifetime interest substantially, and it slows equity accumulation in the years when most borrowers actually sell. The full breakdown is here.

We cover these as they happen in a monthly email — the changes that affect what you'll pay, with the math worked out rather than summarized.