Lease expiries stack, and the year they stack in is the risk
Weighted average lease term is a single number describing a distribution, and distributions hide their shape. The year that matters is the one with the most rent rolling in it.
An average is not a schedule
Two buildings can publish the same weighted average lease term of 3.1 years. In one, every lease rolls in year three. In the other, they are spread evenly across years one to six.
The first is a refinancing problem and the second is not. WALT cannot tell them apart, and it is the number most rent rolls lead with.
Weight it by rent, not by count
Four small suites expiring in one year is not the same event as one large one. The only useful expiry schedule weights each lease by the rent it carries, which is why WALT is weighted in the first place — and why an unweighted count of expiries is close to meaningless.
It also has to include the vacant space. A suite with no lease has no expiry, and quietly leaving it out of the denominator makes every remaining share look larger.
Then line it up against the loan
The question is not whether the leases roll. They always roll. It is whether they roll before or after the loan matures.
A five-year loan on a building whose income rolls in year four is a building that has to be re-let and re-financed at the same time, in whatever market exists then. That is the shape worth finding before you own it.
Every figure above is asserted against the calculation engine in walt-example.test.ts — the same code a live deal runs.