Value controls. The full value range fits within the slider bar: slide toward the top to increase and toward the bottom to decrease, then release to apply. Home values move in $10,000 ticks from $500,000 to $2 million, $100,000 ticks to $3 million, then $1 million ticks. Down-payment ticks use one-fifth of those values, capped at the home price. Rates move in 0.025% ticks from 5% to 9%. Use Enter amount for precise values within these ranges.

Payment chart. The three stacked bands show taxes, home insurance and HOA along the bottom, then monthly principal (including extra payments), and interest / profit above. Drag across the chart to inspect a month. Early payoff reduces payments; taxes and insurance continue. Ownership costs are held flat in this chart and continue after payoff. Maintenance is excluded.

Mortgage. Fixed-rate monthly amortization. Extra payments reduce principal starting in month one. Interest / profit totals exclude taxes, insurance and fees. Property tax and insurance are estimates, not location-based quotes. PMI is excluded throughout the model, assuming at least 20% down. Lower-down-payment insurance costs are not modeled. Taxes and insurance continue after payoff. For Islamic financing, verify the amortization and early-payoff terms with your provider.

Rent vs. buy. Both paths start with the same current investment balance, linked to the Buy down payment until edited separately. The renter invests the entered amount at month-end after paying the entered rent and other expenses. The buyer invests that amount plus the current rent, less the monthly payment from Buy (including extra principal, HOA, and taxes and home insurance when enabled), plus the estimated monthly tax savings when enabled. Buying deducts only the down payment from starting investments. Purchase closing costs and any down-payment cash shortfall are funded separately and deducted from buyer wealth as an upfront cost; it does not divert monthly investment contributions. A zero remaining investment balance starts growing with the first month's contribution.

Future rent and included ownership costs grow at their editable rates. When the mortgage is paid off, the buyer can invest the freed-up payment. Maintenance and renters insurance are excluded by default; enable them under Fine-tune to include those costs. If the monthly buying budget is negative, existing investments cover the gap first. Unfunded gaps reduce buyer wealth without accruing interest; future savings cover those gaps before being invested. Buyer wealth is investments plus home value minus the unpaid mortgage, selling costs and additional cash needed. It is not the full home value plus investments without accounting for the loan.

Tax savings. We assume a new qualifying acquisition mortgage and a $200,000 California salary with married filing jointly status. The 2026 federal standard deduction is $32,200; the California estimate uses the $11,412 deduction and 2025 brackets specified by its 2026 estimated-tax instructions. We apply progressive brackets to taxable income, comparing ownership with renting. Eligible mortgage interest is limited using average outstanding debt: $750,000 federally and $1 million for California. Principal, extra repayments and insurance are not interest deductions. Property tax follows the Buy inclusion setting and the comparison’s cost-growth assumption. State income tax and property tax share the federal SALT cap; we account for lower state income tax when calculating federal deductions. SALT starts at $40,400 in 2026, rises 1% annually through 2029, then returns to $10,000 in 2030 under current law. We hold salary, brackets and standard deductions constant over the projection; future law and inflation may change the outcome. No home-office, PMI, points, payroll-tax deductions, tax credits, AMT or other deductions are modeled. Verify interest deductibility for alternative financing. Savings are estimated annually and invested in twelve equal monthly amounts; disabling the tax option removes them entirely.

Tax references: IRS mortgage interest · 2026 federal rules · California estimates · Home-office eligibility

Bubble Simulation. This optional illustration replaces normal investment returns with a smooth market decline from 100% to 20% during years 3–4. The same market changes apply to both investment portfolios, never to home value or the loan. Contributions continue at month-end and experience only subsequent market changes. After year 4, normal monthly compounding resumes from the remaining investment balances. The market decline is 80%; a portfolio's net fall may differ because contributions and withdrawals continue. It is a stress test, not a forecast.

The horizon is 30 years. Dotted break-even markers interpolate where the monthly wealth lines meet; year labels are approximate. Returns, taxes, and costs are assumptions, not forecasts.

No capital-gains taxes, rent deposits, utilities, extraordinary repairs, refinancing or opportunity costs on other savings are modeled. Assumptions are scenarios, not forecasts or financing offers.

Reference calculators: Zillow mortgage calculator ↗ · NerdWallet rent vs. buy ↗