It is the same limit, whether you shop online or in-store.

Online:

You can spend from 500 (£2.50) to a maximum of 40,000 (£200) Nectar points in one transaction. You’ll need to spend your points in 500 point/£2.50 increments (unless your points cover the entire purchase price and the total falls below the maximum points threshold).

In-store:

You can spend from 500 (£2.50) to a maximum of 40,000 (£200) Nectar points in one transaction. You’ll need to spend your points in 500 point/£2.50 increments (unless your points cover the entire purchase price and the total falls below the maximum points threshold).

Find out more about Nectar at Argos