PHP number_format gotcha

December 19th, 2009

Warning: This post is 13 years old. Some of this information may be out of date.

Be careful when doing any kind of calculations with numbers that have been passed through PHP's number_format function as they can lead to unexpected results. The problems lie with the thousands separator (or the decimal separator if you use anything other than '.'). Here's an example:

andrew@adele:/$ php -a
Interactive shell

php > $number = 1234.56;
php > echo $number;
php > $number = number_format($number, 2);
php > echo $number;
php > echo $number * 100;
php >

The issue is that the calculation ignores everything after the thousands separator ' , '.