If you bought furniture for £4,500 in 2021 and £6.200 in 2022, you will receive the following discounts:
YEAR 2021
£ 4.500 x 1.0 = £ 4.500 in discount income.
£ 4.500 x 0.06 = £ 270 discount.
YEAR 2022
£ 6.200 x 1.0 + £ 4.500 x 0.5 = £ 8,450 in discount income.
£ 5.800 x 0.06 + £ 2,650 x 0.07 = £ 533,5 discount.
YEAR 2023
£ 6.200 x 0.5 = £ 3,100 in discount income
£ 3,100 x 0.06 = £ 186 discount.
Total discount 2021-2023
£ 989,5 which corresponds to 9.2%.