The hCG levels calculator uses the following equations for the several measurements that can be performed on two subsequent beta hCG samples:
A) Absolute difference = Second β-hCG level - First β-hCG level

B) Percentage difference = Absolute difference / First β-hCG level x 100

C) Doubling time = Time between tests in hours / log2 (Second β-hCG level / First β-hCG level)

D) One-day increase = (2(24 / Doubling time in hours) - 1) x 100

E) Two-day increase = (2(48 / Doubling time in hours) - 1) x 100