With the weeks and days rate engine, you can specify that each day is charged as a percentage of the rate set up against the product. The rate against the product is considered a full week’s charge.
Charging periods
Charges for this rate are calculated as a percentage of the weekly rate. For your reference, the leading rental period is listed here as 100%, i.e. the rate you entered against the product.
In the “Days” field, specify the percentage you’d like to charge for each day after the first week.
The number of days is calculated up to 100%. For example, if days are set to 50% and a rental is 3 days, Current will charge 100% (max days), rather than 150% (3x 50% days).
Example
Here’s an example rate definition:
Days: 30%
Weeks: 100%
Assuming a rate against a product of $100 and a quantity of 1:
 For a one day rental, the charge would be $30.
 For a three day rental, the charge would be $90.
 For a six day rental, the charge would be $100; the days percentage exceeds 100% so a full week is charged.
 After one week and two days, the rate will be $160.
Options
Day type

Calendar day
The number of days to charge is based on whole days; the start & end times aren’t taken into consideration. 
24 hour clock
The number of days to charge is based on 24 hour periods; the start & end times are used to calculate rental charging.
For example, a rental that starts January 2nd at 11am and finishes on January 3rd at 9am would be considered two days rental when using “calendar day” since it falls over two whole days, and would be one day of rental because the end time is earlier than the start time.
Rental days per week
Use this option to determine whether weekend days are considered chargeable. If you do not charge for Saturday or Sunday set this to 5, otherwise leave at the default value of 7.
Minimum rental days
The minimum number of days to charge, for example if this was set to 2 and an opportunity started and finished on the same day, Current will charge for two days as a minimum.
Keep in mind that if you enable chargeable days on an opportunity, Current will ignore the minimum rental days.
Leeway minutes
This option is only used when the day type is set to 24 hour clock. It adds a grace period or tolerance to the end of a rental.
For example, if a rental that starts January 2nd at 11am and finishes on January 3rd at 11:30am then the total rental period is 1 day and 30 minutes. This is considered two days of rental charge. However, if you set 60 leeway minutes then the same period would be considered one day of rental charge as 30 minutes is less than the leeway minutes.