Concept of Interest Coverage is akin to Concept of Margin of Safety

INTEREST COVERAGE

Interest Coverage:  This is the number of times that interest charges are earned, found by dividing the (total) fixed charges into the earnings available for such charges (either before or after deducting income taxes).

Interest Coverage
=  Earnings (before or after income tax) / total interest charges



MARGIN OF SAFETY

Margin of Safety, in general, is the same as "interest coverage."

Formerly used in a special sense, to mean the ratio of the balance after interest, to the earnings available for interest.

Margin of Safety
= Balance of earnings after interest / Earnings available for interest.

For example:

Interest  $100
Earnings  $175

Interest cover $175/$100 = 1.75x
Balance after interest = $175 - $100 = $75

The margin of safety (in this special sense) becomes
= $75 / $175
= 42.86%