To top up something

I’d like to know which sentence is correct to use when I’m at a Costa shop handing a member card to a barsta.

“I’d like to top up 10 pounds please.”

or

“I’d like to top up for 10 pounds please.”

• The “for” version makes the 10 pounds the cost of the top-up service rather than the amount to add to your account. Commented Jan 5, 2019 at 1:40
• "Top up" refers to filling some container to the (reasonable) limit. It makes no sense when you use it to mean "add this amount". It might make sense if the intent is to "fill" the card so that it carries the specified total amount, but it would be confusing at best. Commented Jan 5, 2019 at 12:54
• There are two things you might want to do in this situation, either you want to add ten pounds to the balance already on the card or you want to raise the balance on the card to ten pounds. In the first case I would say "I'd like to top up by ten pounds" and in the second I would say "I'd like to top up to ten pounds". Commented Oct 3, 2019 at 8:13
• I tend to agree with @HotLicks here. The word "top" seems completely out of place. Idiomatically, to "top-up" something means to fill it to the top, from where it is currently at -e.g. the oil in your car's engine.
– WS2
Commented Jan 30, 2020 at 13:16
• @BoldBen What's wrong with "Please would you add £10 to the balance on my card" or "Please would you increase my balance to £10"?
– WS2
Commented Jan 30, 2020 at 13:21

Both proposed formulations are ambiguous. They make it unclear whether (1) the amount of the addition is supposed to be 10 pounds (regardless of what is already in the account), or (2) the total in the account, after the addition, is supposed to be 10 pounds (i.e. one wants to add whatever amount will bring the total to 10 pounds). The clearest way of saying (1) is 'I'd like to add 10 pounds'; if one wants (2) one can say 'I'd like to top up to 10 pounds' or if one wants to completely remove any possibility of misunderstanding ''I'd like to bring the balance up to 10 pounds'.

The phrase top up carries the idea of some limit, top, that is to be reached, an therefore fits only (2); it would be confusing to use it if (1) is what one intends. But if (2) is what one intends, then the preposition that should be used before the limit is to, not for.

“I’d like to top up for 10 pounds please.” or “I’d like to top up 10 pounds please.”

Either sentence would work, especially in the context of one proffering a card to a barista and stating such.

top up TFD

(Banking & Finance) to add money to (a loan, bank account, etc) in order to keep it at a constant or acceptable level