Liver fibrosis is an excessive grouping of scar tissue which results in the ongoing inflammation and liver cell death. Here is the fibrosis-4 (fib-4) formula to calculate the fibrosis of Liver based on the fibrosis four index. As per the fibrosis-4 (fib-4) formula, to calculate the value, initially, multiply the age with aspartate aminotransferase. Take square root of alanine and multiply with platelets. Now divide the step 1 value by step 2 to get the result.