Calculators

Additional payment calculator
How much do you save by paying more or making additional payments than your initial mortgage terms?

Monthly payment calculator
Want to know how much your monthly payment is for your mortgage?

How much do I have to earn?
Not sure how much money you'll have to earn to afford your house payment and accompanying expenses?

How much can I borrow?
Want to know how big of a mortgage you can take on?

Should I pay discount points?
Not sure if you should pay discount points on your mortgage loan?

How much will I save by refinancing my loan?
How long will it take to recoup the costs of refinancing my home mortgage?

How much will my tax deduction be?
Want to know how much your home mortgage will save you in taxes?

Biweekly mortgage calculator
Want to know how much time and money you'll save paying off your loan on a biweekly payment plan?

APR calculator
To find out the annual percentage rate of your loan, enter the loan amount, interest rate, points, other costs and yearlength term.

Interest only monthly payment calculator
To find out the monthly savings you could gain from an interestonly payment plan.

Mortgage Calculations by Hand
Learn the formulas for calculating interest rates and payments.
Mortgage Calculations by Hand
First you must define some variables to make it easier to set up: P = principal, the initial amount of the loan I = the annual interest rate (from 1 to 100%) L = length, the length (in years) of the loan, or at least the length over which the loan is amortized.
The following assumes a typical conventional loan where the interest is compounded monthly. First we'll define two more variables to make the calculations easier: J = monthly interest in decimal form = I / (12 x 100) N = number of months over which loan is amortized = L x 12
Now for the big monthly payment (M) formula ... it is:
J M = P x  1  ( 1 + J ) ^ N where 1 is the number one (it does not appear too clearly on some browsers)
So to calculate it, you would first calculate 1 + J then take that to the N (minus N) power, subtract that from the number 1. Now take the inverse of that (if you have a 1/X button on your calculator push that). Then multiply the result times J and then times P.
The oneliner for a program would be (adjust for your favorite language):
M = P * ( J / (1  (1 + J) ** N))
So now you should be able to calculate the monthly payment, M. To calculate the amortization table you need to do some iterations (i.e. a simple loop). Here are the simple steps :
Step 1: Calculate H = P x J, this is your current monthly interest
Step 2: Calculate C = M  H, this is your monthly payment minus your monthly interest, so it is the amount of principal you pay for that month
Step 3: Calculate Q = P  C, this is the new balance of your principal of your loan.
Step 4: Set P equal to Q and go back to Step 1: You thusly loop around until the value Q (and hence P) goes to zero.
Many people have asked how to find N (number of payments) given the payment, interest and loan amount. The answer to the actual formula is in the book: The Vest Pocket Real Estate Advisor by Martin Miles (Prentice Hall). Here's the formula:
N = 1/Q * (LN(1(B/M)*(R/Q)))/LN(1+(R/Q))
Where:

Q = amount of annual payment periods

R = interest rate

B = principle

M = payment amount

N = amount payment period

LN = natural logarithm