The court's ruling, dated May 12, was published on Wednesday.
On April 1, the Supreme Rada voted overwhelmingly for presidential elections to be held on October 25, three months ahead of the date President Viktor Yushchenko had pushed for.
Yushchenko, whose popularity ratings have fallen to single figures amid political instability and a shrinking economy, turned to the Constitutional Court on April 8.
In line with the new version of the Constitution that entered into force in 2006, presidential elections are held on the last Sunday of the last month of the president's fifth year in office. This would be January 17, 2010, the date Yushchenko had insisted on.
However, MPs decided that as the current head of state took office in 2005, which was prior to the new version of the Constitution taking effect, the old regulations should be effective. Under the previous Constitution, elections are held on the last Sunday of October.
Analysts say the decision to call elections for October 25 was dictated by fears that the president could dismiss parliament.
Yushchenko's former "Orange Revolution" ally, current Prime Minister Yulia Tymoshenko, now an arch-rival, is likely to run against him in the polls, whenever they eventually take place.
Tymoshenko said Wednesday that she believed Yushchenko had secured several more months to work on his election campaign.
"The president has haggled for a few more months from the Constitutional Court," she told journalists.
