Setting the base rule: how many points a purchase earns

The base rule is your standard conversion from amount spent to points, for example 1 point for every 1 spent. It applies to every unit transaction first, before any other earn rules you've added.

New accounts start with 1 point for every 1 unit, in proportional mode. If that works for you, there's nothing to change.

Change the base rule

Go to Loyalty → Earn rules.
On the Unit transactions card, click Open rules.
If your account has more than one unit, click the page title, for example Rules: Purchase amount, and pick the unit you want to change.
On the Base rule card, click the row with your current rule, for example "1 point(s) for every € 1.00".
Fill in the sentence "Every [currency] [amount] equals [n] Points". For example, 10 and 1 gives 1 point for every 10 spent.
Choose the Operation (see below).
Click Submit.

The number of points must be a whole number. Whether the amount can have decimals, for example 2.50, depends on your unit: a unit with decimals allows them, a whole-number unit doesn't.

Every unit has its own base rule, so changing it for one unit doesn't change the others. A unit you haven't set a base rule for yet starts with the same values as your first one.

Strict or proportional

Proportional mode (the default): contacts earn points in proportion to what they spend. With 1 point for every 10, a purchase of 25 earns 2.5 points before rounding.
Strict mode: only whole multiples of the amount count. With 1 point for every 10, a purchase of 25 earns 2 points, and a purchase of 9 earns nothing.

How fractions are rounded

Points are always whole numbers, so fractions are rounded. How that happens depends on Settings → Rounding type in the sidebar of the unit transaction rules. The default is Round down, so 2.5 points becomes 2. See How to configure earn rules for the other options.

Orders have their own base rule

This base rule only applies to unit transactions: transactions that come in as an amount. If your integration sends orders, those are handled by order rules, which have a separate base rule. See Setting up order rules.

What goes wrong

Contacts earn fewer points than expected. Check the Operation. In Strict mode, anything below the amount earns nothing and the remainder is dropped. Also check Rounding type.
Contacts earn more points than the base rule says. Your advanced rules run after the base rule and change its result. See How to configure earn rules.
Changing the base rule has no effect. You may have changed the base rule of another unit: check the unit in the page title. Or the purchase came in as an order rather than a unit transaction, so check the base rule under Orders too.