Mortgage Calculator

Disclaimer

I make no guarantees of correctness. I am not a financial planner. Use this at your own peril.

Note: If there is more than one way to specify an amount (i.e. as a percentage of something else, or an absolute amount), and more than one (non-zero) value is provided, then the calculator uses whichever value is listed first.

FYI: all inputs are saved, so refreshing the page won’t clear them. Some inputs are saved in the URL (so a given visualization is easy to share); others are saved in localStorage (so that they don’t get shared if you copy the URL).

If you’re curious how things are calculated, you can look at the derivations (see the checkbox below), or read the source.

Costs

Home Price: $
Home’s Assessed Tax Value: $
HOA: $ /mo
Down Payment: % or $
Interest Rate: %
Points purchased:
Value of a point: %
Mortgage Insurance: $ /mo
Mortgage Insurance stops at equity: %
Property Tax: $ /quarter or %/yr
Residential exemption: $ /yr or $ deducted from home value
Taxes Collected Start (month only):
Homeowners Insurance: $ /mo
Principal Pre-payment: $ /mo
Closing Cost: $
Mortgage term: yrs
Recurring Monthly Debts: $

Income/assets

Gross Annual Income: $
Total Assets: $

What have you already paid?

Closed already? Yes
Payments already made: or closing date:
Model at month (leave blank for “now”):

Misc.

Assumed average rate of return of stocks: %/yr

Payment Info

Show derivations?
Simplify derivations?

Amount of loan:

Principal and Interest:

Annual property tax:

Average Monthly Expenses:

Average Monthly Expenses (with mortgage insurance):

Months of PMI payments:

Lifetime of loan:

Total paid over life of principal & interest:

Total paid at closing:

Total paid so far:

Equity owned so far:

Total still owed on loan:

Remaining equity to pay for:

Debt-to-income ratio:

Payments made if fired tomorrow:

Opportunity cost

Suppose you have extra each month. Is it better to prepay the mortgage, or invest in stocks?

It depends on the interest rate of the loan vs. the expected return in the stock market.

(Below, "total assets" isn't taken into account; this just focuses on the growth of the "extra" money that can either be used for mortgage prepayments or for investment in the stock market.)

Assets after with prepayments, then investing:
Assets after with minimum payments, simultaneously investing:

Changelog:

2024/01/07: Don't actually hide non-computable outputs.
2022/03/31: Add expandable table to show interest paid in a given tax year.
2021/10/03: Add expandable payment schedule tables.
2021/09/05: Add comparison between loan prepayments and stock investment.
2021/09/04: Add support for monthly loan prepayments.
2021/08/09: Fix off-by-one bug in cumulative payments. Compute remainder owed on loan, and equity still to be paid for.
2021/07/25: Store sensitive inputs in cookies, rather than the URL, for privacy.
2021/06/17: Add support for computing burndown after closing/having made some payments.
2021/04/25: Expose the payment schedule in the DevTools Console.
2021/03/29: Add support for buying points.
2021/03/28: Add burndown countdown.
2021/03/27: PMI only applies if down payment is < 20%.
2021/03/27: Incorporate residential exemption savings to property tax calculation.
2021/03/03: Make PMI stopping point configurable. Add label to show how long PMI payments last, and how much total is paid toward PMI.
2021/02/02: Add debt-to-income calculation.
2021/01/10: Add support for varying the mortgage term.
2021/01/03: Added ability to specify property tax as annual percentage. Added ability to explicitly specify home value (for calculating property tax). Removed extraneous fields from cumulative payment chart. Added ability to specify down payment as a dollar amount.
2020/12/20: Added cumulative payment chart.
2020/12/15: Initial post with monthly payment breakdown chart.

Written on December 14, 2020

Programming || math