The lease renewal notices that landlords send out annually have contained little good news for renters in recent years: Rents are up and vacancies down around the country. And having resigned themselves to paying more, renters may wonder whether the new number on their lease was plucked out of thin air.

Rest assured, it was not.

For about a decade the country’s biggest landlords, who together control about a million rental apartments, have been using powerful software tools to set rental rates on new and renewing leases. Patterned after the technology used to price airline tickets and hotel rooms, the software weighs competitors’ rental rates, market conditions, seasonal trends and hundreds of other variables to recommend the highest feasible rent for each apartment at a given time.

The technology can benefit residents as well. Just as travelers can lower their airline fare by flying at off times, residents can often lock in lower monthly rents by agreeing to lease terms that help apartment owners avoid downtime or fill less popular units. Revenue management software can generate options for renters by varying rental rates, start dates and numbers of months on the lease — and still hit a landlord’s revenue target.

Now landlords with as few as 3,000 units are testing the technology, which is chiefly produced by two companies, the Rainmaker Group of Alpharetta, Ga., which sells a program called Rainmaker LRO (for lease rent options); and RealPage Inc., of Carrollton, Tex., which calls its version YieldStar Price Optimizer. Both products incorporate data collected automatically from competitors along with masses of market and property information. YieldStar adds data from RealPage’s market researcher, MPF Research.