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An amortization schedule will help you understand your monthly payments and fit them into your budget. The benefit of creating your own spreadsheet is that you can save it on your own computer and print it out, which you can't do with the online calculators.  Most basic spreadsheet apps have amortization table templates built in. You also may be able to find a template for the spreadsheet app you use and download it for free online. Using a template will save you from having to enter the amortization formula manually. Your spreadsheet will have a separate line or row for each payment over the life of the loan. You may want to organize your spreadsheet so that the first half of the payments are on one side of the page and the other half run down the other side of the page, so you can see the whole table at a glance. The first column of your spreadsheet typically should be the date each payment will be made. Work with your spreadsheet functions to see if you can get these dates to auto-populate based on a formula rather than having to input each one manually. The two columns that provide the amount of each payment that goes to principal and the amount that goes to interest will be the most useful columns for you in comparing different loans or understanding how your loan is amortized.  In the beginning, you'll notice that more of your payment goes to interest than to principal. This is because interest is being computed on a larger amount of principal initially. As you pay down the principal, the interest you pay gradually decreases as well and more of your payment goes to principal. If you aren't using a specifically designed amortization table spreadsheet, you'll have to enter the code yourself for the amortization formula so that your spreadsheet will auto-populate these columns and you don't have to calculate each amount by hand. You may want to add an additional column for the interest rate. If you have a fixed-rate loan, you may feel this column is unnecessary, but it could be useful if you have an adjustable-rate loan. Unless you have an adjustable-rate loan, your monthly payments aren't going to change, so you can easily fill in the payments column using cut and paste.  Your overall balance typically should be the last column on the spreadsheet. Use the formula function to fill in the data for this column, showing the balance decline by the amount of each monthly payment. You also may want to include a column that shows how the principal balance (rather than the total payoff amount) is declining over time. To populate this column, create a formula that subtracts the amount of each payment applied to principal from the total remaining principal after each payment. If you have a fixed-rate loan, your amortization schedule will determine the amount of each monthly payment. This amount won't change unless you are late with a payment, at which point your lender will charge you late fees and other penalties.  Some lenders reserve the right to increase the interest rate if you are late on multiple payments, which could affect the amount of your monthly payment. Keep in mind that if you are late on a mortgage payment, you typically must continue to pay fees and penalties until your mortgage is brought current. This means if you skip one month's payment and then make the regular monthly payment the next month, you'll be charged for two months of late fees. In many cases, you can make extra payments each month and these will be applied entirely to the principal of your loan. Making extra payments, whether regularly or sporadically, can help reduce the amount of interest you have to pay. You'll also pay off your loan faster. With an amortization schedule you can create an extra column for extra payments. Enter extra payments to see how much sooner you can pay your loan off.
Download a template. Create a line for each payment. Include the date of each payment. Add columns for principal and interest. Set columns for your balance and payments. Make your payments on time. Evaluate the impact of extra payments.