About
The 30% rule: rent + utilities should be under 30% of gross income. Modern reality: HCOL cities may require 35-50%. The 28/36 rule is stricter: housing 28%, total debt 36%.
The 30% threshold was codified into US housing policy by the 1969 Brooke Amendment to the Housing Act, which capped public-housing rents at 25% of tenant income (raised to 30% in 1981) and became the de facto definition of "rent-burdened" used by HUD and most landlords today. The "40x rule" most NYC and Bay Area landlords now use is the same idea rearranged: annual gross income must be at least 40 times the monthly rent (so a $3,000 rent requires $120,000 income, which is exactly 30%). Zillow's 2025 Consumer Housing Trends Report finds that 52% of US renters are now cost-burdened (>30% of income) and 27% are severely burdened (>50%). HUD's 2025 Fair Market Rent for a 2-bed in San Francisco-Oakland sits at $3,476, in Manhattan at $4,164, against a national median of $1,789. That makes the 30% rule literally impossible for median renters in the top tier of HCOL metros without two incomes or a roommate.
Formula
Frequently asked questions
How accurate is the Rent Affordability Calculator?
It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.
Is the Rent Affordability Calculator free to use?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.
Are my inputs saved anywhere?
No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.
Can I use the Rent Affordability Calculator on my phone?
Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum.
Does the Rent Affordability Calculator work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
How do I report a bug or suggest improvement to the Rent Affordability Calculator?
Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours.
Can I share results from the Rent Affordability Calculator?
Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.
Why are the results different from another rent affordability tool?
Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.
Is the Rent Affordability Calculator accurate?
The Rent Affordability Calculator applies the standard formula for rent affordability. Accuracy is limited only by your input precision. For decisions with material consequences, use the result as a starting point and verify with a qualified professional or the relevant official source.
Is the Rent Affordability Calculator free?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads that appear around the tool but not inside the calculation flow.
Are my inputs saved?
No. Inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but does not see what you type into the form.
Should I use gross income or net (take-home) for the 30% rule?
Landlords and HUD use gross. Personal-finance educators (Ramit Sethi, NerdWallet) increasingly argue for using net income because two earners with identical $100K gross can have a $20K-$30K take-home gap depending on state, 401(k), and health-premium deductions. A working safer threshold: 30% of gross for HCOL, 25% of net for everyone else. If your effective tax + retirement contribution rate exceeds 30%, switch to the net version.
What does the 40x rule mean and why do landlords use it?
The 40x rule states that annual gross income must be at least 40 times the monthly rent. It is mathematically identical to the 30% rule (1/12 divided by 30% equals 40), but landlords prefer it because the income test is easy to verify off a W-2 or offer letter. A $2,500 rent therefore needs $100,000 annual income; $4,000 needs $160,000. NYC, San Francisco and most of greater Boston use 40x as the standard underwriting threshold; lower-rent markets often relax to 35x or 30x.
How to use the Rent Affordability Calculator
The Rent Affordability Calculator is a browser-based tool that runs entirely on your device. Inputs you enter never reach a server - all calculations happen client-side in JavaScript. This means:
- Privacy: nothing is logged, sent, or stored by 3Tej. Inputs disappear when you close the tab.
- Speed: results update as you type. No network round trip.
- Offline use: once the page is cached, it works without internet.
- No signup: no account, no email, no rate limits.
Step by step
- Enter your inputs in the form above. Each field is labeled with its unit (currency, percent, kg, etc.) and the expected range.
- Read the result as it updates. The number reflects the formula commonly accepted in Rent Affordability-related calculations.
- Adjust to see sensitivity: change one input at a time and watch how the output moves. This is the fastest way to understand which variable matters most.
- Copy or screenshot the result for later reference. The page state persists for the session if your browser allows it.
When you would use this
- Quick estimates: when you need a number now and don't want to open a spreadsheet.
- Sensitivity analysis: testing how a result changes as inputs vary, before committing to a real-world decision.
- Comparison: running the same calculation with different inputs to compare options side by side.
- Learning: building intuition for how the underlying math behaves.
- Documentation: capturing a snapshot of inputs and outputs at a point in time.