if(empty(prop("Booking Period")), 0, max(1, dateBetween(dateEnd(prop("Booking Period")), dateStart(prop("Booking Period")), "days")))

Rental days between pickup and return. Picking up on the 5th and returning on the 8th is three days, not four — the same convention hotels use for nights. The minimum of one day means a same-day rental still charges.

the Daily Rate of the linked Vehicle

The price the car rents for, read straight off the vehicle. Price a car once in the fleet and every future booking of it is already priced.

if(empty(prop("Rate Override")), prop("Vehicle Daily Rate"), prop("Rate Override"))

The rate this booking actually charges. It is the vehicle's own rate unless Rate Override is filled in, so the normal case needs no typing and the negotiated case is still one number away.

((if(empty(prop("Booking Period")), 0, max(1, dateBetween(dateEnd(prop("Booking Period")), dateStart(prop("Booking Period")), "days"))) * if(empty(prop("Rate Override")), prop("Vehicle Daily Rate"), prop("Rate Override"))) + prop("Extras")) - prop("Discount")

What the rental costs. Both the day count and the effective daily rate are recomputed inside this formula rather than read from Duration Days and Daily Rate, because Notion's formula engine cannot read one formula from inside another.

(((if(empty(prop("Booking Period")), 0, max(1, dateBetween(dateEnd(prop("Booking Period")), dateStart(prop("Booking Period")), "days"))) * if(empty(prop("Rate Override")), prop("Vehicle Daily Rate"), prop("Rate Override"))) + prop("Extras")) - prop("Discount")) - prop("Amount Paid")

What the renter still owes. Zero means settled. Negative means you have taken too much.

sum of Net Paid across every linked Transaction

Not a formula but a rollup, which is why you never type into it. Log the payment as a Transaction linked to the booking and this number updates itself — that is what makes the money reconcile.

if(and(prop("Security Deposit Held") > 0, !prop("Deposit Returned")), prop("Security Deposit Held"), 0)

How much of the renter's money you are still holding. A security deposit is not income — it is their money sitting with you until you give it back.

if(prop("Status") != "Completed", 0, if(prop("Type") == "Refund", -prop("Amount"), if(or(prop("Type") == "Income", prop("Type") == "Deposit"), prop("Amount"), 0)))

Decides what each transaction contributes to a booking. Pending payments do not count. Refunds subtract. Business expenses never touch a renter's balance.

if(empty(prop("Type")), "", ((((if(prop("Type") == "Income", "💵 ", if(prop("Type") == "Deposit", "🔒 ", if(prop("Type") == "Refund", "↩️ ", "🧾 "))) + prop("Type")) + if(empty(prop("Category")), "", " · " + prop("Category"))) + if(empty(prop("Amount")), "", " · " + format(prop("Amount")))) + if(empty(prop("Booking Ref")), "", " · Booking #" + format(prop("Booking Ref")))) + if(empty(prop("Transaction Date")), "", " · " + formatDate(prop("Transaction Date"), "D MMM YYYY")))

Names the transaction from its own fields, emoji included — 💵 for income, 🔒 for a deposit, ↩️ for a refund, 🧾 for an expense. Money records are the ones you log fastest and name worst, so the system writes the description instead of asking you to.

prop("Revenue") - prop("Maintenance Cost")

What this car has actually made, once its repairs are counted against it. Compare against Purchase Price to judge the investment.

min(if(empty(prop("Insurance Expiry")), 9999, dateBetween(prop("Insurance Expiry"), now(), "days")), if(empty(prop("Registration Expiry")), 9999, dateBetween(prop("Registration Expiry"), now(), "days")), if(empty(prop("Roadworthiness Expiry")), 9999, dateBetween(prop("Roadworthiness Expiry"), now(), "days")), if(empty(prop("Next Service")), 9999, dateBetween(prop("Next Service"), now(), "days")))

The soonest of the four compliance dates. A blank date is parked at 9999 days so it cannot win the comparison, and a negative number means that deadline has already passed and the car should not be on the road.