Interest begins on the day the final judgment is entered. If partial payments are made, those payments are first applied to the accrued interest and then to the unpaid principal.
To calculate the interest, first determine the daily amount of interest. For example, a $10,000 judgment accrues $1,000 of interest per year at a rate of 10 percent. Dividing $1,000 by 365 days gives you a daily interest rate of $2.73. Now, assume that after 145 days the debtor pays you $2,000. The following computation shows the amount of interest that will accrue after that payment is made:
After 145 days, $395.85 (145 days x $2.73/day) of interest will have accrued on the $10,000 judgment. Out of the debtor’s $2,000 payment, pay yourself the accrued interest first. You then will have $1,604.15 left ($2,000 - $395.85 = $1,604.15). Now credit the remaining $1,604.15 against the $10,000 judgment ($10,000 - $1,604.15 = $8,395.85 of unpaid principal). The new daily interest will then accrue at a rate of $2.30/day ($8,385.85 x 10% = $839.58 ÷ 365).
Assume, then, that 215 days later a $750 payment is made. During the 215 days, $494.50 (215 days x $2.30/day) of interest will have accrued. Out of the $750, pay yourself the accrued interest first ($750 - $494.50 = $255.50) leaving $255.50 to apply to unpaid principal. Now credit the $255.50 against the remaining judgment principal of $8,385.85, and we find that $8,130.35 remains unpaid. The new daily interest will then accrue at a rate of $2.22/day ($8,130.85 x 10% = $813.03÷ 365).