Why was more of my last HELOC payment applied to interest?

Under the terms of your HELOC agreement, payments will be applied first to all interest accrued when we receive the payment. Because interest accrues daily, the amount of interest that may accrue from payment to payment can vary based on the number of days in the month, the number of days since the last payment, and the amount of principal. So, if more interest accrued since your last payment, more of your payment will be applied to interest.