half-life

noun \ ˈhaf-ˌlīf , ˈhäf- \
Updated on: 13 Oct 2017

Definition of half-life

1 : the time required for half of something to undergo a process: such as
a : the time required for half of the atoms of a radioactive substance to become disintegrated
b : the time required for half the amount of a substance (such as a drug, radioactive tracer, or pesticide) in or introduced into a living system or ecosystem to be eliminated or disintegrated by natural processes
2 : a period of usefulness or popularity preceding decline or obsolescence
  • slang usually has a short half-life

First Known Use of half-life

1907


Financial Definition of HALF-LIFE

half-life

What It Is

In the investing world, a half-life is the halfway point of mortgage repayment.

How It Works

Let's say John Doe borrows $100,000 to buy a house. The interest rate is 4% with  a 30-year mortgage. His monthly payment is $477.42, which includes some interest and some principal.

By building an amortization schedule, we can see that John will have to make 231 mortgage payments (roughly 19 years) before half of his loan is paid off.

Why It Matters

The half-life of any debt depends on the terms of the debt. In John's case, each payment includes interest and principal. In the early years of his loan, his payments are largely interest. As time passes, however, more of his payment is principal repayment. Accordingly, the half-life is not 50% of the time involved, but 50% of the principal involved. Note that John's interest rate and loan length influence the half-life tremendously.


HALF-LIFE Defined for English Language Learners

half-life

noun

Definition of half-life for English Language Learners

  • : the time it takes for a radioactive substance to lose half its radioactivity


HALF-LIFE Defined for Kids

half-life

noun \ ˈhaf-ˌlīf , ˈhäf- \

Definition of half-life for Students

plural half-lives \-ˌlīvz\
: the time required for half of the atoms of a radioactive substance to change composition

Medical Dictionary

half-life

noun \ -ˌlīf \

medical Definition of half-life

: the time required for half of something to undergo a process: as
a : the time required for half of the atoms of a radioactive substance to become disintegrated
b : the time required for half the amount of a substance (as a drug or radioactive tracer) in or introduced into a living system or ecosystem to be eliminated or disintegrated by natural processes
  • the serum half-life is about 2 days
  • Journal of the American Medical Association


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