Vedic Astrology has a method of providing a fairly good indication of compatibility based on nakshatras (Lunar Constellations) of prospective husband and wife. It assigns points (guna) for factors that influence marriage. Although, neither this site, nor the whole process is the final say on compatibility issues (guna milap), it can be a good starting point.
Apart from determining the number of Gunas that match in the two horoscopes, there are other factors that should be taken into consideration: longevity, health, wealth, children and overlapping Vimshottari dashas.
Horoscope Compatibility: You can enter date, time and place of birth for prospective husband and wife in this guna milap application software and match the charts. It determines the number of Gunas matching in the two horoscopes. It also determines whether they are Manglik and if their Manglik Dosha cancels.
To see an explanation of the horoscope matching (guna milap) system, click here : Chart Matching Fundamentals. For an explanation on Manglik Dosha, please see Clarifications on Manglik Dosha and Manglik Dosha and Chart Matching. Further reading – the missing Tara element.