Add and subtract 3 month from a given date time

I have this start date : 2023-09-03T00:00:00+05:30
and end date : 2023-09-10T00:00:00+05:30

I want to subtract 90 days from start date and add 90 days from end date

and then convert it to UTC format

for that I was using this function in angular

moment(startStr, 'YYYY-MM-DD hh:mm:ss').utc().format('YYYY-MM-DD hh:mm:ss');
moment(endStr, 'YYYY-MM-DD hh:mm:ss').utc().format('YYYY-MM-DD hh:mm:ss');

How can I do that?

>Solution :

For moment you can use add and substract functions. Example below:

var startDate = moment(startStr, 'YYYY-MM-DD hh:mm:ss');
var endDate = moment(endStr, 'YYYY-MM-DD hh:mm:ss');

startDate =  startDate.subtract(90, 'days');
console.log(startDate);
endDate =  endDate.add(90, 'days');
console.log(endDate);

// then do your utc conversion

Reference material:

moment add function link

moment subsctract function link