Day Counting

This provides a consistent and accurate way of pricing any securities that have an interest rate component.
Different securities use different conventions to count the days.

Actual / Actual	US Treasury Bonds, US Treasury Notes, US Treasury STRIPS
Actual / 360	US Treasury Bills, LIBOR floating rate
365 / 360
360 / 365
30 / 360	Corporate Bonds, Municipal Bonds

US 30/360

If the first date is the last day of February, then first date is changed to 30
If the first date has 31 days, then first date is changed to 30 days
If the first date has 30 or 31 days and second date has 31, then second date is changed to 30 days
If the first date is the last day of February and second date is the last day of February, then second date is changed to 30 days

European 30/360

If the first date has 31 days, then first date is changed to 30 days
If the second date has 31 days, then second date is changed to 30 days

Fixed Rates are generally quoted as actual/365 or 30/360

An individual would rather be paid interest based on actual/360 rather than 30/360 because, on average there are more than 30 days in a month.