Kemm għandu żmien il-Qamar bejn wieħed u ieħor, u allura l-fażi bejn wieħed u ieħor, nistgħu nikkalkulawh għal kull data billi ngħoddu l-ġranet minn data magħrufa ta' qamar mitluf (pereżempju l-1 ta' Jannar 1900 jew il-11 ta' Awwissu 1999) u nirriduċu dan in-numru modulo 29.530588853 (it-tul tax-xhar sinodiku). <includeonly>ThedifferencePerò betweendan twoil-kalkulu datesjissoponi canl-orbita behija calculatedċirku byperfett subtractingu thegħalhekk [[Julianirridu day|Juliannikkoreġuh Daybi Number]]ftit of one from that of the other, or there are simpler formulae giving (for instance) the number of days since December 31, 1899. However, this calculation assumes a perfectly circular orbit and therefore may be incorrect by several hourssigħat <includeonly>(it also becomes less accurate the larger the difference between the required date and the reference date); it is accurate enough to use in a novelty clock application showing moon phase, but specialist usage taking account of lunar apogee and perigee requires a more elaborate calculation.
