My shipping company charges a fixed amount up to 5KG, then a fixed fee per KG above 5. For example, items up to 5 kg would cost 5 euros, whereas for every extra KG, the cost is +0.5 euro. So for an item 6kg, the cost would be 5 + 0.5=5.5 euros.

I have setup the costs to be:

0-5KGs: 5 euros

5KGs and up: 0.5 euros per KG.

However, if an item is 6kg, the costs calculation is made as 6 x 0.50 = 3euros (instead of 5 + 0.5=5.5 euros)

For an item of 10KG, it calculates 10 x 0.50 = 5euros (instead of 5 + 2.5 = 7.5 euros)

Am I doing something wrong? How can I setup this cost calculation?

Thanks in advance