Lopez, who turned 48 on Monday, and Rodriguez, who turns 42 on Thursday, rang in the occasions at a lavish bash with friends Saturday in Miami.
"Happy birthday to Us!!! #leos #305," Rodriguez captioned a photo on Instagram of himself and Lopez at the fête.
The retired New York Yankees star also shared videos on Instagram Stories of himself and Lopez standing next to their six-tier birthday cake, dancing with friends and sharing kisses on the dance floor.
"#305," he captioned one post, referencing the area code for Miami.
People reported Lopez and Rodriguez continued the celebrations Sunday by stepping out to Prime 112 restaurant for a romantic dinner. The couple were first linked in March, and confirmed their relationship the same month.
"Things are great with them," a source told People in June. "Jennifer still gushes about Alex every chance she gets. The more she gets to know him, the more she likes him. They are definitely very serious."
Lopez shares 9-year-old twins Emme and Max with ex-husband Marc Anthony, while Rodriguez is dad to two daughters, 12-year-old Natasha and 9-year-old Ella, with ex-wife Cynthia Scurtis. Rodriguez treated Natasha to one of Lopez's concerts in June.
"[Their kids have] really bonded and become good friends," an insider told E! News in April. "A-Rod's older daughter, Natasha, is like a big sister to J. Lo's twins."