In the finance world quarter 1 usually spans January 1-March 31; quarter 2 usually spans April 1-June 30; quarter 3 usually spans July 1-September 30; and quarter 4 usually spans October 1-December 31.
For companies that operate on a calendar year basis, here's a closer look at a few recent and upcoming quarterly periods, along with the Q1, Q2, Q3, or Q4 reference associated with each period:
Q1 2018 -- January 1, 2018 to March 31, 2018
Q2 2018 -- April 1, 2018 to June 30, 2018
Q3 2018 -- July 1, 2018 to September 30, 2018
Q4 2018 -- October 1, 2018 to December 31, 2018
Q1 2019 -- January 1, 2019 to March 31, 2019
{{{Q2 2019 -- April 1, 2019 to June 30, 2019}}}
Q3 2019 -- July 1, 2019 to September 30, 2019
Q4 2019 -- October 1, 2019 to December 31, 2019
Q1 2020 -- January 1, 2020 to March 31, 2020
Q2 2020 -- April 1, 2020 to June 30, 2020
Q3 2020 -- July 1, 2020 to September 30, 2020
Q4 2020 -- October 1, 2020 to December 31, 2020