Does Splitit reserve the full amount on my credit card?

Yes.

The full amount of your purchase is authorized (held) on your credit card to guarantee future payments to your merchant or retailer so you need to have at least that in available credit on your card. This allows us to offer our service to the merchant or retailer without applications or credit checks. Splitit does not charge interest or fees; even if you pay late (although your credit card provider might so please check).

As long as your payment plan is kept up to date, these authorizations are never charged.

Authorizations are renewed every 17-21 days and the amount reduces with each monthly payment you make until the balance is cleared. The previous authorization is removed as soon as the new one is obtained.