Semi Monthly Dating

I am creating an amortization schedule for a Canadian mortgage.

Attached is a copy of the spreadsheet.

I want to have dates displayed for payments. Annual, semi-annual, quarterly, monthly, semi-monthly, biweekly and weekly. All of the dating except for semi-monthly has gone smooth. I even tried to put a list of dates in column A (and hide them with white text) and use that for my date display in Column C. If anyone can help me either reconstruct my IF statement in Column C so that the Semi Monthly dates will appear or be able to generate a listing of semi-monthly dates in Column A, I would greatly appreciate it.

I want to be able to enter ANY date in Cell O8 (example 3/4/2011). The next date could be 3/18/2011 or 3/19/2011 (it doesn't matter to me if it goes up by 14 or 15 days). Then, the days of the month stay constant. So in other words, the dates would go:
3/4/2011
3/18/2011
4/4/2011
4/18/2011
5/4/2011
5/18/2011

I have found several spreadsheets/tips online that take the inputted date and force the payments to be at the beginning and middle or middle and end of the month. I'd rather not go down that road if I could help it.

Thanks so much for any help given

In C5:
=C4+14

In C6 downwards:
=DATE(YEAR(C4),MONTH(C4)+1,DAY(C4))

?

Thanks for the reply guys.

However, both of those suggestions skip months. In other words, they'll do two payments in month 2 and then do two payments in month 4.

Still looking for some help - appreciate any feedback!

Thanks!

Yeah, both mine and Roger's solutions work fine, not sure what you're doing wrong?

Type the Date 3/4/2011in C4
Copy the formula in C5
=DATE(YEAR(C4),MONTH(C4),DAY(C4)+14)

Apply this logic

Yes! I was doing something wrong indeed.

Thanks again for the wonderful help