Thanks, this works nicely indeed and moved the data to a table, holding all possible combinations of sex, months and weight. I am trying to work out what the best way is to get the centile from the input data as the provided months and weight won't be in the table. So for example months 6, weight 8 how would I get the centile. One option is to take the nearest months and weight and I can do that, but ideally I would make it proportional to get the more accurate centile as if it was taken from a chart. I can do this in code, but I would like to do it in SQL and not sure how to do that. RBS