I'm trying to get the next 'renewal date' of a subscription model (month & year). That's my setup:

var getPeriod = 'month';
// var getPeriod = 'year';

var getEffective = '2022-06-02';
var getDate = moment('2022-08-01');

if(getPeriod == 'month'){
    var getDuration = moment.duration(getDate.diff(getEffective)).months();
} else if('year'){
    var getDuration = moment.duration(getDate.diff(getEffective)).years();
}

if(getDuration >= 0){
    var getCounter = getDuration+1;
} else {
    var getCounter = 1;
}

var getRenewalNext = moment(getEffective).add(getCounter, getPeriod+'s').format('YYYY-MM-DD');

console.log('getDuration:');
console.log(getDuration);

console.log('getRenewalNext:');
console.log(getRenewalNext);

Attempt 1: Correct

var getEffective = '2022-06-01';
var getDate = moment('2022-08-01');

"getDuration:"
2
"getRenewalNext:"
"2022-09-01"

Attempt 2: Correct

var getEffective = '2022-06-03';
var getDate = moment('2022-08-01');

"getDuration:"
1
"getRenewalNext:"
"2022-08-03"

Attempt 3: Not Correct

var getEffective = '2022-06-02';
var getDate = moment('2022-08-01');

"getDuration:"
2
"getRenewalNext:"
"2022-09-02"

For the last attempt I'm getting "2022-09-02" as the next renewal data, but I would have expected 1 more day to go and 'Next Renewal Date' to be "2022-08-02". Why so or am I missing something? How can I solve this?

That's my fiddle: https://jsfiddle.net/ja1k6owb/