Add columns to the transaction-level data showing the accident year and the development lag

Create a pivot table showing cumulative accident year insured loss:

Rows = accident year

Columns = development period

Data = cumulative sum of Amount

Use your pivot table to create and format a loss development triangle, exclude any partial accident years (in this dataset 2017is a partial year)

Compute the link ratios from the development triangle

Select average link ratios

Use your link ratios to "square" the triangle and estimate ultimate losses

Compute factor to ultimate (FTUs)