Answer by taking a quote from the following article:

Harriet Tubman (born Araminta Ross, c. 1822 - March 10, 1913) was an American abolitionist. Born into slavery, Tubman escaped and subsequently made some thirteen missions to rescue approximately seventy enslaved people, family and friends, using the network of antislavery activists and safe houses known as the Underground Railroad. She later helped abolitionist John Brown recruit men for his raid on Harpers Ferry.

By 1840, Tubman's father, Ben, was manumitted from slavery at the age of 45, as stipulated in a former owner's will, though his actual age was closer to 55. He continued working as a timber estimator and foreman for the Thompson family, who had held him as a slave. Several years later, Tubman contacted a white attorney and paid him five dollars to investigate her mother's legal status. The lawyer discovered that a former owner had issued instructions that Rit, like her husband, would be manumitted at the age of 45. The record showed that a similar provision would apply to Rit's children, and that any children born after she reached 45 years of age were legally free, but the Pattison and Brodess families had ignored this stipulation when they inherited the slaves. Challenging it legally was an impossible task for Tubman.  Around 1844, she married a free black man named John Tubman. Although little is known about him or their time together, the union was complicated because of her slave status. Since the mother's status dictated that of children, any children born to Harriet and John would be enslaved. Such blended marriages - free people of color marrying enslaved people - were not uncommon on the Eastern Shore of Maryland, where by this time, half the black population was free. Most African-American families had both free and enslaved members. Larson suggests that they might have planned to buy Tubman's freedom.  Tubman changed her name from Araminta to Harriet soon after her marriage, though the exact timing is unclear. Larson suggests this happened right after the wedding, and Clinton suggests that it coincided with Tubman's plans to escape from slavery. She adopted her mother's name, possibly as part of a religious conversion, or to honor another relative.

When did Harriet first run away?