How to get value of form field and past it to another form field - yii

Question

I am developing HR system, I want to calculate how many days off the employee can take.
In the HR table I have three attributes.
1- start_date(when the employee starting to work in the company).
2- leavestaken(how many days off the employee took before).
3- leaves(the number of days available for the employee to take off) which equal to=(months between current date and start_date) * 2.5(beacuse each month give 2.5 days off) - leavestaken
third attribute is automated and not from the user, how I can get the first and second attributive values from field forms, use them in the calculation and save the result in the leaves attribute?
I'm using sql and this only for server side

Answer 1

Server side:
If your start_date is unix timestamp:
if ($model->load(Yii::$app->request->post())) {
n_month = (time() - $model->leaves) / (30 * 24 * 60 * 60);
$model->leaves = ceil(n_month * 2.5) - $model->leavestaken;
# code...
//ceil : Because one day off is not complete, Rounds a number down to the nearest integer
But if it's not unix, you can use the date_diff() method or ...
You can do this in the model file, in the beforeSave or beforeValidate method.
You can use JavaScript to calculate the client side.

Answer 2

My solution was
if ($model->load(Yii::$app->request->post()) ) {
$date = date('m/d/Y');
$datetime1 = date_create($date);
$datetime2 = date_create($model->start_date);
// calculates the difference between DateTime objects
$interval = $datetime2->diff($datetime1);
$n_month= $interval->m + 12*$interval->y;
$model->leaves = ceil($n_month * 2.5) - $model->leavestaken;
$model->save();