Since February I have added the recitation of the Roman Martyrology to my '62 daily Divine Office, I have the book but it has been hard to figure out the day of the moon in the lunar cycle. Here is an easy way to know, it is on your regular wall (solar) calendar!
Every normal calendar indicates the new moon, which will always be the day before your luna prima.
And remember that the martyrology always is anticipatory, so that, for example, you will recite the martyrology of Friday, 8th of April (Sexto Idus Aprilis, Luna Prima) on Thursday, 7th of April.
In other words, the martyrology always commemorates the Luna Prima on the New Moon (the previous day)!
Today we recite the Luna Vicesima Quinta of Sunday, 3rd of April (Tertio Nonas Aprilis).
There are 29.5306 days in a lunar cycle.