Availability is calculated per day and per unit from the bookings that already exist, not from a single stock number. This means a fleet can be partly booked in one period and completely free in another, and the product page answers correctly for both situations.
For example, consider a fleet of three kayaks. If two are booked in June and two are booked in July, all three are still available in August. Each month is evaluated independently against the bookings on record for that period.
WooCommerce's stock arithmetic is left entirely alone for outright sales and is bypassed for rental lines. A rental occupies dates rather than reducing a stock count. Without this separation, the system would refuse a booking for dates that are genuinely free, simply because units are booked on other dates.
Using the same three-kayak example: two units booked in June and two units booked in July would appear to WooCommerce's standard stock logic as four units consumed from a fleet of three, causing it to block one of those bookings. FW Rental for WooCommerce bypasses that arithmetic for rental lines, so each period is checked independently and both bookings go through correctly.
If a product's stock is not managed in WooCommerce, FW Rental for WooCommerce treats it as having no upper limit on units. Shops that do not track stock numbers for their rental items need not change anything — the product will accept bookings without restriction based on unit count.
Two shop-wide settings determine which orders count against availability. Both are found at WooCommerce > Settings > Rental:
The unpaid hold prevents two shoppers from checking out with the same dates at the same time. Once the hold period expires without payment, the dates are released and become available again.
When Show availability is enabled in the shop settings, the product page displays how many units are free for the dates a shopper has chosen. Fully booked days are shown as unavailable on the calendar. On catalogue and category pages, once dates have been chosen using the site-wide date picker, each rental product shows whether it is free for those dates and what it would cost.
Every availability figure is calculated on the server from live booking data, so the number a shopper reads matches what the cart will accept.