Building future date array - php

Question

I am building an interactive web form where after user logs in, they can choose to pay toward their account...either every (n)th day of the month OR every 'n' number of days - and they will choose how many payments they'd like to do
They will use datepicker to choose their starting date (which can never be sooner than tomorrow)
I want to pass these parameters to a php script and then render a page that says they have agreed to make x number of payments on the following dates....
I'm having a problem getting the math right that I pass to this script.
i.e. if they choose to make 6 payments every 14 days starting on 6/25/2017 for example....how do I put this in an array and have the resulting page say: you've agreed to pay x amount on:
06/25/2017
07/09/2017
07/23/2017
08/06/2017
08/20/2017
09/03/2017
etc
They can choose a minimum of 1 payment date or up to a max of 12 payment dates. Can someone steer me in the right direction on building the array?

Answer 1

You should add x days to your inicial date, one way is:
$next = date("Y-m-d", strtotime('+ 14 days', strtotime($initialdate)));

Answer 2

Give this a shot...
<?php
// the date the user selected
$selectedPaymentDate = strtotime('2017-06-24');
// the frequency a user will pay
$freqNum = 14;
$freqType = 'days'; // days, months, years, whatever `strtotime` will handle
// the total number of payments a user must make
$totalPayments = 6;
// where we'll keep the dates
$paymentDates = [];
// build the dates array
for($i = 0; $i <= $totalPayments; $i++){
$next = ($freqNum * $i);
$paymentDates[]= date('Y-m-d', strtotime("+{$next} {$freqType}", $selectedPaymentDate));
}