What is the expected date of delivery (EDD) if the LMP is Jan 30?

If you subtract 3 months from January wouldnt that be October?
January; December (1 month), November (2nd month), October(3rd month)...
Or is it because it is later on in January so the whole month counts?
Do we need to take into consideration that January can have 31 days, so adding 7 days could make the day on the 6th?
And even if you add 9 months (normal gestation period) after the Jan. 30 you get the month October:
Jan-Feb (1), Feb-Mar (2), Mar-Apr (3), Apr-May (4), May-Jun (5), Jun-Jul (6), Jul-Aug (7), Aug-Sept (8), Sept-Oct (9).