Akshaya Tritiya is one of the most significant days, both, according to the Hindu calendar and mythology. Calendar wise, it falls on the third day of the bright half of Vaishakha (late April - early May), when the sun and the moon are in exalted positions and at the peak of their brightness. Such a phenomenon happens only once a year and is astrologically considered the perfect time to start any successful business.
As per mythological legends that are linked to the day, it proved to be nothing but fruitful to many: sacred river Ganga descended onto the earth from heaven, Lord Parashurama, the sixth incarnation of Lord Shiva being born, Pandavas getting unlimited supply of food from the Akshaya Patra, and Sudama getting blessed by Lord Krishna more than he could have asked for; all happened on this day.
According to the Sanskrit meaning of the word Akshaya: imperishable or never diminishing, the fruits that are borne on this day, keep on multiplying. It's precisely because of this reason and another, according to which the day is ruled by the Preserver God Vishnu, that any venture: be it a business or any personal quest for self realization gets fulfilled positively.
Lord Vishnu sees the intention and preserves what has been started. On this day, people buy and wear gold: an ultimate symbol of wealth and prosperity, which is believed to invite the Goddess of wealth, Laxmi, into the households. It's even considered an auspicious time to make long term purchases in the form of gold or silver, real estate, diamonds and other precious stones, and shares and bonds. 21st April marks Akshaya Tritiya in the year 2015.