A home affordability calculator on iPhone runs entirely in your mobile browser and applies the 28/36 debt-to-income rule — housing capped at 28% of gross income and total debt capped at 36% — to estimate the maximum home price you can carry from your income, debts, and down payment without installing anything from the App Store. The calculator works backward from your finances to find the largest mortgage payment you can sustain, then converts that ceiling into a maximum loan using inverse amortization and adds your cash down payment on top to reveal the affordable home price. Because every input lives in your browser tab, you can experiment with different incomes, debt totals, rates, terms, and down payments and watch the three output numbers — affordable home price, affordable loan amount, and maximum monthly housing payment — recalculate the moment you change any field. No app updates, no in-app purchases, no account creation, no permissions to grant, and nothing you type is uploaded, saved, or shared with a third party.
Why a Browser-Based Home Affordability Calculator Beats an iPhone App
Most people who search for a home affordability calculator on iPhone end up on the App Store, where dozens of apps advertise the same three numbers. The trade-off is real: many of those apps ask for an account, push notifications, subscriptions, or location and contact permissions you don't actually need to estimate a mortgage payment. A browser-based calculator skips all of that. Open the page in Safari, fill in the form, and you get an answer without giving up any permissions, your email, or storage space on your phone.
Two practical reasons this matters on a phone. First, the math runs locally, which means your salary, debt balances, and savings figures never leave the device. If you're shopping for a home and don't want your income shared with an ad network or a third-party SDK, that local-only processing is a real privacy win. Second, there's nothing to update. Mortgage rates shift, lending rules adjust, and apps that haven't been touched in a year can quietly fall out of date; a browser page refreshes every visit, so the math reflects what the page currently does, not what it did when the app was last approved.
The other benefit is portability. If you switch from iPhone to iPad to a friend's laptop mid-search, the same page renders the same way. There's no sync, no platform lock-in, and no lost history if you clear Safari's cache. For a one-time financial decision like buying a home, that's a more useful shape than another icon on your home screen.
How to Use the Home Affordability Calculator on iPhone
Open the calculator in Safari and the form lives on a single scrollable page. Tap each field, type with the iPhone keyboard, and the results update as soon as you tab to the next box. Here's the order to work through.
- Open the Home Affordability Calculator in Safari on your iPhone and tap the income field. Enter your gross (pre-tax) income and use the toggle to mark it monthly or annual — the calculator converts annual to monthly automatically.
- Add up your recurring monthly debts in the next field: the car payment, student loan minimum, and the total minimum payment across all credit cards. Skip one-time balances or medical bills that aren't part of your regular monthly outflow.
- Move to the loan section. Enter the cash you have ready for a down payment, your expected mortgage interest rate as a percentage (for example 6.5), and the loan term in years — typically 15 or 30.
- Read the three numbers the calculator returns: the affordable home price, the affordable loan amount, and the maximum monthly housing payment. Each one recalculates the moment you change any input, so you can adjust and re-read without leaving the page.
- To compare scenarios — a 15-year versus 30-year term, a larger down payment, or paying off a debt first — change one input at a time and watch the affordable home price move. There's no save button because the math lives in the browser, not on a server.
The 28/36 Rule Behind the Numbers
The number on your screen is the output of two ratios and one reverse mortgage calculation. Understanding both pieces helps you read the result as a budget rather than a target.
The 28/36 rule sets two ceilings on your monthly budget, both expressed as percentages of your gross (pre-tax) monthly income. The front-end ratio caps housing costs at 28%. The back-end ratio caps all recurring monthly debt — including the future mortgage — at 36%. Your maximum housing budget is whichever of those two numbers is smaller: min(0.28 × income, 0.36 × income − other monthly debts).
When your other debts are low, the 28% front-end ratio usually binds. When debts are high (a car payment plus student loans, for example), the 36% back-end ratio pulls the ceiling down. If your existing debts already exceed 36% of your income, the ceiling drops to zero and the calculator returns no affordable home price — a signal that debt paydown should come before house hunting.
Once the monthly ceiling is set, the calculator converts it into a loan amount using inverse amortization: with r = annual rate ÷ 12 and n = years × 12, the maximum loan is payment × ((1 + r)^n − 1) ÷ (r × (1 + r)^n). That loan, plus your cash down payment, is the affordable home price. The two ratios are widely cited as lender guidelines; the U.S. Consumer Financial Protection Bureau describes them as the standard benchmarks most mortgage underwriters use (see the CFPB explanation of debt-to-income ratios), and Wikipedia's debt-to-income ratio entry traces the same 28/36 front-end and back-end definitions.
A quick worked example with simple inputs. Take a gross monthly income of $4,000 and assume no other monthly debts. The front-end ceiling is 0.28 × $4,000 = $1,120. The back-end ceiling is 0.36 × $4,000 − $0 = $1,440. The smaller number is $1,120, so the maximum monthly housing payment is $1,120. At 5% over 30 years, that payment supports a loan of roughly $208,600 — and with a $20,000 down payment, the affordable home price comes out around $228,600. Change any input and the whole result moves with it.
Inputs and Outputs at a Glance
The calculator keeps the inputs short on purpose. Three numbers describe your finances, two describe the loan, and three outputs come back. The table below shows what each field is and what it controls.
| Type | Field | What it controls |
|---|---|---|
| Input | Gross income (monthly or annual) | Drives both the 28% and 36% ceilings |
| Input | Total recurring monthly debts | Lowers the 36% ceiling when present |
| Input | Cash down payment | Added directly to the loan to form the home price |
| Input | Annual interest rate (%) | Sets the discount rate for inverse amortization |
| Input | Loan term (years) | Sets the number of monthly periods |
| Output | Affordable home price | Loan + down payment; the headline number |
| Output | Affordable loan amount | The mortgage you can carry under the rule |
| Output | Max monthly housing payment | The ceiling the calculator applied (28% or 36%) |
What the Result Doesn't Include
The affordable home price is a clean number, but it covers principal and interest on the loan only. Your real monthly housing bill typically adds four other line items, and any of them can shrink the price you can comfortably carry.
Property taxes vary by county and can run from a few hundred dollars a year to several thousand on a more expensive home. Homeowners insurance is usually quoted annually and rolled into the monthly escrow payment. Private mortgage insurance (PMI) is required by most lenders when the down payment is below 20% of the home price, and it adds a percentage of the loan to each monthly bill. HOA dues apply in many condos, townhomes, and planned communities, and they live entirely outside the mortgage math.
A quick sanity check: if your lender quotes taxes and insurance totaling $300 a month and you're at the $1,120 housing ceiling, the principal-and-interest share drops to $820, which supports a smaller loan and a smaller affordable price. The calculator doesn't know your local tax rate, so it can't subtract that for you. Treat the result as a principal-and-interest ceiling and add the other costs on top before you commit to a search range.
When the Number Shifts (and How to Recalculate on iPhone)
The affordable home price isn't a fixed fact — it's a snapshot of your finances today under one set of assumptions. Six common moves change it.
A higher down payment adds cash directly to the affordable price without raising the monthly payment. Paying off a car loan or a credit-card balance removes a recurring debt, which can lift the 36% back-end ceiling and free up housing budget. Switching from a 30-year to a 15-year term lowers the maximum loan because the same monthly amount has to amortize over fewer periods. A lower interest rate stretches the loan amount upward for the same payment, which raises the affordable price. A higher income obviously lifts both ratios. And dropping recurring debt to zero can shift the binding constraint from the 36% back-end back to the 28% front-end.
Because every field recalculates instantly, you can run all six of these experiments from the same Safari tab. The fastest workflow is to change one input, read the new affordable price, change it back, then move to the next input. There's no save state, no submission, and no waiting — and for a more thorough breakdown of how income alone drives the result, the guide to calculating home affordability based on income walks through the same ratios from a slightly different angle.
After you've narrowed the range, take the three output numbers to a licensed mortgage professional for confirmation. The 28/36 rule is a guideline, not a guarantee — real underwriting also weighs your credit score, cash reserves, employment history, and the specific loan program (FHA, VA, and conventional loans each use different limits, and some lenders stretch ratios higher). The calculator gives you a credible starting benchmark; a lender gives you the actual approval number.
For a deeper look, see Car Loan Calculator on Mac: Run It in Safari or Chrome.