I tested it this time, I messed up the brackets:
$calc( 500 + 100 * $floor( $calc( ( X / 3 ) - 1 ) ) ) ;correct
$calc( 500 + 100 * ( $floor( $calc( X / 3 ) - 1 ) ) ) ;wrong
raw USERNOTICE:*:{
if ($msgtags(room-id).key == 12665) && (resub isin $msgtags) {
if (($msgtags(msg-param-months).key) >= 3) {
msg $1 !bonus $msgtags(display-name).key $calc( 500 + 100 * $floor( $calc( ( $msgtags(msg-param-months).key / 3 ) - 1 ) ) )
}
}
}
><;; hopefully there won't be any need for further edits