When starting to learn JavaScript, the book "JavaScript, The Definitive Guide" published by O'Reilly had a working example of a formatted page to calculate the payment on a loan for a given amount, interest rate, and number of payments. I streamlined the formula, changed the length of the loan to include months as well as years, and added a Principal-Interest table to show how much of each payment was interest and how much went into paying down the loan. That also shows what it would take to pay off the loan at any point.

Goes Into Not needed a much now but at one time you could find out the balance

Federal 2017 withholding schedule From Publication 15, Circular E, Employer's Tax Guide from the IRS, this page shows what should be withheld for married/single, number exemptions, salary, and pay period. It extrapolates the salary into an annual amount, calculates withholding based on the annual schedule, and divides back into the number of pay periods per year. Previous years are provided for reference.

Federal 2018 withholding schedule New from an interim document. Use at your own risk.