Computed fields and rollups

A total copied by hand is wrong the next day. A due date entered twice drifts. A counter updated manually always ends up lying.

Whenever one piece of data follows from another, it does not have to be typed.

Two ways to calculate

A formula looks at the other fields on the same record. An amount before tax and a rate give an amount including tax. A signature date and a duration give a deadline.

A rollup looks at the linked records. A client's revenue comes from the sum of their invoices. A company's number of contacts comes from the count of its contacts.

The difference comes down to one question: is the information already on the record, or do you have to go and fetch it from the neighbouring ones?

A rollup needs a relation

This is what blocks people most often. To total a client's invoices, the invoices have to be linked to that client. Not carrying its name as text: linked.

If the rollup you want is not offered, the relation is almost always missing upstream. Create it, and the rollup becomes possible.

A computed field is not typed in

There is no box to fill. The value appears, updates when its sources change, and you cannot overwrite it.

When not to calculate

A computed field depends on its sources. If those are incomplete, it passes the gap along instead of flagging it.

For data that stands as the reference, a negotiated price, a contractual amount, a figure validated by a third party, an ordinary field is the better choice: you fill it in, and it does not move on its own.