How to change date_popup date format in form?
EDIT: fixed by setting up drupal date format and using datepicker_options:

$form['mymodule_start_date'] = array(
'#type' =&gt; 'date_popup',
'#title' =&gt; t('Start date'),
'#date_format' =&gt; 'd-m-Y',
'#datepicker_options' =&gt; array(
    'maxDate' =&gt; 0,
    'dateFormat' =&gt; date_popup_format_to_popup('d-m-Y'),
    ),
'#date_year_range' =&gt; '-3:+0',
'#date_label_position' =&gt; 'above',
'#theme_wrappers' =&gt; array('date_popup'),
'#required' =&gt; TRUE, 


);