What formula is used by lenders in calculating P&I?

What formula is used by lenders in calculating P&I?

Member since 2022 路 17 posts 路 3 votes

Seems like it should be a simple formula, but my googling is failing me... I'm trying to figure out what a lender uses to calculate the following:

Inputs: mortgage balance (after downpayment), interest rate, and loan term

Output: monthly payment (principle and interest)

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Malcomb StapelPro Member
Investor 路 Topeka, KS 路 Member since 2020 路 669 posts 路 488 votes
4y
Quote from @Tom Seigold:

Seems like it should be a simple formula, but my googling is failing me... I'm trying to figure out what a lender uses to calculate the following:

Inputs: mortgage balance (after downpayment), interest rate, and loan term

Output: monthly payment (principle and interest)


 Is it not as simple as plugging it into a mortgage calculator? I'm guessing you could even Google an amortization calculator if you wanted to break it down by payment over the length of the loan. 

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  • Malcomb StapelPro Member
    Investor 路 Topeka, KS 路 Member since 2020 路 669 posts 路 488 votes
    4y
    Quote from @Tom Seigold:

    Seems like it should be a simple formula, but my googling is failing me... I'm trying to figure out what a lender uses to calculate the following:

    Inputs: mortgage balance (after downpayment), interest rate, and loan term

    Output: monthly payment (principle and interest)


     Is it not as simple as plugging it into a mortgage calculator? I'm guessing you could even Google an amortization calculator if you wanted to break it down by payment over the length of the loan. 

  • Ned CareyPro Member
    Moderator
    Investor 路 Baltimore, MD 路 Member since 2008 路 17k+ posts 路 13k+ votes
    4y

    @Tom Seigold it is not a simple calculation. What is simple as mentioned above is use a mortgage amortization schedule. Again as said above just enter, amount, interest rate the the number of years into an Amortization schedule and it will spit out your answer. 

    Amortization is the rate at which a loan is paid down. You may have heard that interest is front loaded, or that you pay more interest up front in a 30 year loan, but that is deceiving. It implies that banks somehow manipulate what is owed up early in the mortgage. The reality is you pay the exact same rate for the entire loan. However that is hard to calculate, because the amount you owe changes every month. 

    An amortization chart takes it all into consideration and makes the answer easy. 

  • Rental Property Investor 路 Columbus, OH 路 Member since 2017 路 3k+ posts 路 3k+ votes
    4y
    Quote from @Tom Seigold:

    Seems like it should be a simple formula, but my googling is failing me... I'm trying to figure out what a lender uses to calculate the following:

    Inputs: mortgage balance (after downpayment), interest rate, and loan term

    Output: monthly payment (principle and interest)

    Hi Tom, this is the calculation website I use for my real estate here in Columbus and Cincinnati area. It gives you P &I based on your imputs.
    https://www.calculator.net/ren...

  • Member since 2022 路 17 posts 路 3 votes
    4y

    Thanks everyone.  The reason I'm looking for a formula instead of using an online tool is because I'm developing some software for my personal use where I want to implement this formula, so that I can import a property and see (among many other things existing calculators/spreadsheets don't offer) what the monthly payment would be.

    EDIT: I ended up finding it here:

    https://stackoverflow.com/ques...

  • NY 路 Member since 2021 路 143 posts 路 45 votes
    4y

    @Tom Seigold

    You want formulas instead? Pretty sure I just did it in Google sheets last time because I wanted to double check the numbers. Wasn't down to the cent but fairly close.

  • NY 路 Member since 2021 路 143 posts 路 45 votes
    4y

    @Tom Seigold

    Can give me some hypothetical or actual numbers to check if my formulas still work

  • Member since 2022 路 17 posts 路 3 votes
    4y
    Quote from @Eddie L.:

    @Tom Seigold

    You want formulas instead? Pretty sure I just did it in Google sheets last time because I wanted to double check the numbers. Wasn't down to the cent but fairly close.

    That would be awesome if you can send them over.  I'm not sure how accurate this other code I found is.
  • NY 路 Member since 2021 路 143 posts 路 45 votes
    4y

    Can't seem to attach files here... After inputting below formulas just drag Row14=Payment Period/Principal/Interest/Total/Net Balance down to Row 373 for 360 Payment Periods

    Monthly payment of $2,147.29=B3*((E3/12)*(1+E3/12)^B5)/(((1+E3/12)^B5)-1)

    Payment Period of 1 =A13+1

    Principal of $480.62=$B$7-C14

    Interest of $1,666.67=E13*$E$3/12

    Total of $2,147.29=sum(B14:C14)
    Net Balance of $399,519.38=E13-B14


    Sale Price$500,000.00
    Down Payment$100,000.0020.00%
    Loan Balance$400,000.0080.00%Interest Rate5.000%

    Loan Term360

    Monthly Payment$2,147.29

    LTD Total$400,000.00$373,023.14$773,023.14


    Payment PeriodPrincipalInterestTotalNet Balance
    0$400,000.00
    1$480.62$1,666.67$2,147.29$399,519.38
  • Member since 2022 路 17 posts 路 3 votes
    4y

    Thanks Eddie 馃槉

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