The method used to distribute a cost equally over its period is straight-line.

For example, an asset is bought for 96,000 and its useful life is 10 years (120 months). The straight-lining of its cost will be 800 per month (96,000 / 120). A lease is signed for 2 years (24 months) for a yearly payment of 12,000 but a free rent period is agreed for the first 6 months. Hence the payments will be 6,000 + 12,000 = 18,000. The straight-lining of the cost of the lease will be 750 (18,000 / 24). Here the payment won't match the cost and that's the purpose of the straight-lining method of cost allocation: first 6 months payment 0 and cost 750, remaining 18 months payment 1,000 cost 750.