Tal u Matar is scheduled to start the last night of Chanukah every nineteen years through 2127. Note that in 2051 it starts the night of Dec. 5 (as it advances a day every four years until the extra day in Feb moves it back to Dec 4 at night).
By the way, this takes into account the fact that in 2099, the date to begin will shift Dec 5th at night, and since 2100 will not have a February 29, Tal UMatar will stay that way (Dec 5 most years, Dec 6 every four years) until it shifts to Dec 6 at night in 2199. So actually, in 2146 from what I can tell Tal uMatar actually starts Motzaei Chanuka (Dec 5 at night)!
Two necessary disclaimers: 1. All of these calculations should be rendered moot with the coming of Mashiach and the reestablishment of the Sanhedrin
2. For anyone in EY, these calculations are already moot. After all the last day of Chanukah can’t ever be 7 MarCheshvan!