Our primary financing arrangement is the 2018 credit facility, which provides us with the capital necessary to meet our working capital needs as well as the flexibility to continue with our strategic initiatives, including business acquisitions and share repurchases. The 2018 credit facility will mature in 2023. We also have an unsecured $20 million line of credit used to support our short-term funding requirements of payroll client fund obligations due to the investment of client funds, rather than liquidating client funds that have already been invested in available-for-sale securities. The line of credit, which terminates August 16, 2019, did not have a balance outstanding at March 31, 2019. Refer to our Annual Report on Form 10-K for the year ended December 31, 2018 for additional details of our debt and financing arrangements.

The balance outstanding under the credit facility was $182.0 million and $135.5 million at March 31, 2019 and December 31, 2018, respectively. Interest expense for the three months ended March 31, 2019 and 2018 was $1.4 million and $1.8 million, respectively. We had approximately $210 million of available funds under the credit facility at March 31, 2019, net of outstanding letters of credit of $1.1 million. As of March 31, 2019, we were in compliance with our debt covenants.

Three Months Ended

Weighted average rates

Range of effective rates

2.12% - 5.50%

2.37% - 5.00%