Paid Memberships Pro: Prorated Amount Based on Current Time and Beginning of Next Year

pmpro-prorated-expiration.php

<?php
function pmpro_prorated_checkout_level( $level ) {

	// 5 is the membership level ID.
	if ( 5 === absint( $level->id ) ) {
		$price_per_day = $level->initial_payment / 365.2425; // 365.2425 is the days in a year

		// Get timestamp for end of year and current timestamp.
		$end_date_timestamp = strtotime( 'first day of january next year' );
		$current_date_timestamp = time();

		// Get the time difference.
		$time_difference = $end_date_timestamp - $current_date_timestamp;

		// Ensure non negative values.
		if ( $time_difference <= 0 ) {
			return $level;
		}
		// Convert timestamp to days.
		$days = round( $time_difference / 86400 ); // 86400 is seconds in a day.
		
		// Calculate price left in the year
		$prorated_price = round( $days * $price_per_day, 2 );
		$level->initial_payment = $prorated_price;
	}
	return $level;
}
add_filter( 'pmpro_checkout_level', 'pmpro_prorated_checkout_level' );