func(currYear, currMonth, x) {
	yearDiff = x/12;
	monthDiff = x%12;

	if (currMonth - monthDiff < 0) {
		yearDiff--;
	}

	newMonth = currMonth - monthDiff < 0 ? 12 - (monthDiff - currMonth) + 1 : currMonth - monthDiff;
	newYear = year - yearDiff;

	return ...
}