A monthly interest rate can be included on the promissory note. 4. ALLOCATION OF PAYMENTS: Each payment shall be credited first to any late charge due, second to interest, and the remainder to principal.Here's the information you'll need to have handy to complete your unsecured promissory note, interest-only with balloon final payment. Washington promissory notes should highlight the relevant payment information. Easily draft a personal loan, mortgage, or commercial loan agreement with our downloadable templates, featuring Washington State-specific laws and regulations. If interest is charged, the rate should be included with a repayment schedule.