In the story, Gregor's father reveals that the family is not as financially strained as Gregor imagined. First, Gregor's family still possesses a small inheritance from the past. This inheritance has been allowed to grow in interest.
Additionally, Gregor's family did not spend all of the income Gregor brought home. Gregor's father managed to save a small amount. In fact, this portion has been allowed to accumulate interest, as well.
When Gregor hears this, he is relieved and happy that his father had the foresight to save a small fortune for the family. Gregor does feel a small pang, however. He thinks that the accumulated money could have been used to free himself from a miserable employment situation. It is telling that Gregor's father opted not to give Gregor relief; instead, he chose to keep the savings a secret from Gregor.
According to the story, Gregor's parents had been in debt to Gregor's employer. It was Gregor who worked to free them of this debt. The text tells us that Gregor's work eventually earned him so much money that he was able to bear the burden of supporting his entire family.
Gregor's family was initially grateful for his sacrifice. However, as time passed, they began to take his generosity and sacrifice for granted.