Principal and accrued interest thereon shall be immediately due and payable upon demand of the Lender. Interest shall accrue on the outstanding principal amount at a rate equal to 10% per annum. Interest shall be calculated on the basis of the actual number of days elapsed and a year of 365/366 days, as applicable. Any accrued but unpaid interest shall be added to the principal balance on the last day of each year that the principal is outstanding and unpaid.