I've been considering home ownership, and all other things equal, I'd like to know how much of a mortgage I can afford based on the rent I currently pay.

Not including heat and hot water, I pay roughly $800 a month on a two-bedroom apartment. Most mortgage calculators take the total mortgage you get and calculate how much you'd need to pay per month to get that mortgage - I'd like to take my current monthly payment and find out what the highest rated mortgage is that I could get.

Ideally, I'd like a formula I can adjust - for X monthly payments, over Y years, at Z interest and tax. That way, I can adjust it for any additional budgetary concerns (insurance comes to mind).

So, for $800 a month, over a period of 30 years, at 3.5% interest and tax rates, with 20% down, how big a mortgage can I take out?

  • 1
    A down payment of 10% at the very least is often the minimum required, and if you can put 20% down, your interest rate will be lower. Commented Jun 16, 2015 at 18:35
  • 3
    Don't forget property tax, home owner's insurance, trash, heat, hot water, lights AND repairs.
    – mkennedy
    Commented Jun 16, 2015 at 19:01
  • 3
    What's wrong with guessing plugging numbers into a regular mortgage calculator until you reach $800. I would use 4.5% interest just to stay on the safe side.
    – MonkeyZeus
    Commented Jun 16, 2015 at 19:10
  • 1
    A 200k mortgage over 30 years at 4.5% with 40k down would be ~$810/month
    – MonkeyZeus
    Commented Jun 16, 2015 at 19:13
  • 1
    Look at #1 on this list: cnet.com/how-to/…
    – MonkeyZeus
    Commented Jun 16, 2015 at 19:14

3 Answers 3


I frequently use the Bret Whissel's amortization calculator. Fill in all fields except for one and click calculate. The calculator will figure out the value for the field that was left blank.

For your example, you would be able to take out a mortgage of $178,155.99 ($800/mo for 30 years at 3.5%). You could buy a house for $222,695 with 20% down ($44,539).


If you google around you can find a few calculators that will do what you ask. Here is one from Citibank and here is one from a mortgage company in Connecticut.

These estimate the amount you could borrow. However, that isn't the whole story. As Dilip notes, it will be difficult to get a mortgage with zero down. The less you put down, the higher the interest rate is likely to be, and/or the more strict the lender will be about you debt/income ratio. So even if the calculator says you can geta $200k loan, that doesn't mean you can borrow that amount regardless of other factors (like your down payment).


The calculator I'm familiar with is


The benefit to this is that it calculates not just the actual mortgage payment, but all the extra costs to owning a home, which are extremely important to figure out what you can afford.

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