Calculate revenue difference for a faster site

calc-revenue-diff.php

<?php
/**
 * Calculate the difference in revenue I should experience
 * if my load time changes.
 *
 * Based on the assumption that every second of page load
 * causes a 7% drop in conversions.
 *
 * Formula in LaTex: [ R = \frac{ R_p }{ {e}^{\ln(0.93) T_p} }\  e^{\ln(0.93) T_c} - R_p ]
 *
 * @param float $revenue_current   Current revenue for the site.
 * @param float $load_time_current Current load time for the site.
 * @param float $load_time_new     Projected new load time for the site.
 * @return float                   Projected difference in revenue for the site.
 */
function calc_revenue_gain( $revenue_current = 50000, $load_time_current = 5, $load_time_new = 2 ) {
	$revenue_new = $revenue_current / ( exp( log( 0.93 ) * $load_time_current ) ) * exp( log( 0.93 ) * $load_time_new );
	return $revenue_new - $revenue_current;
}


echo calc_revenue_gain( 50000, 5, 2 ) . PHP_EOL;

echo calc_revenue_gain( 30000, 10, 3 ) . PHP_EOL;