A simple script to calculate compound interest

compound-interest.js

// Input it initial amount
// Interest as a number, e.g. 5% is 1.05 on a yearly basis
// Length as number of years
// Name of this calculation
// Addition determines whether the input variable is one time or a yearly contribution
function compound( input, interest, length, name, addition ) {
	var accumulated = input
	for ( i=0; i < length; i++ ) {
		accumulated *= interest
		if ( addition ){
			accumulated += input
		}
	}
	console.log( name + ' will '+(input > accumulated ? 'grow' : 'shrink')+' from  ' + input + ' to ' + accumulated + ' at ' + interest +  ' over ' + length + ' years' )
}

compound( 500, 1.05, 40, 'sigarettes', true ) // How much money will a habit of cigarettes generate in retirement money?
compound( 750, 1.05, 40, 'coffee', true ) // How much money will a habit of coffee outside the house generate in retirement money?
compound( 3750, 1.05, 40, 'lunch', true ) // How much money will a habit of lunch out the house generate in retirement money?

compound( 500, 1.05, 40, '500', false )
compound( 5000, 1.05, 40, '5000', false )
compound( 5000, 1.07, 40, '5000', false )