The following formulas are used:

Percent Change

((x(t)/x(t-1)) - 1) * 100

Percent Change from Year Ago

((x(t)/x(t-n_obs_per_yr)) - 1) * 100

Change from Year Ago (where the indicator is already in percent. ie: Unemployment Rate)

x(t) - x(t-n_obs_per_yr)

Notes:

'x(t)' is the value of series x at time period t.

'n_obs_per_yr' is the number of observations per year. The number of observations per year differs by frequency:

Annual, 1

Monthly, 12

Quarterly, 4