Increment year and semester mathematically

increment_year_semester.php

<?php
/**
 * Increment year and semester mathematically
 *
 * @param int $year
 * @param int $semester
 * @param int $increment
 * @return string
 */
function increment_year_semester($year, $semester, $increment = 1)
{
    $semester = $semester;
    $year     = floor($year + ($semester + $increment) * 0.5 - 0.5);
    $semester = abs(($semester + $increment - 1) % 2) + 1;
    return "{$year}/{$semester}";
}

for ($i = -5; $i < 5; $i++)
{
    echo "<pre> {$i}: " . print_r(increment_year_semester(2015, 2, $i), TRUE) . '</pre>';
}