Its a terms thing, in a one year lease, let's say you sign it in December, and pay for the month of January. Now each month you make a payment for the "next" mo

Its a terms thing, in a one year lease, let's say you sign it in December, and pay for the month of January. Now each month you make a payment for the "next" month, so in November (month 11) you make the final payment for December. You have made 12 payments but the last one was in month 11. The first payment was made in month "0" :-) it happens "outside" the lease range. In a 99 year lease (the more common ones) you make your first year payment and then the lease starts. Then you make 99 more payments and at the end of the last year the least ends. Which will be the 100 year anniversary of the start of the lease.