base rate

noun3

1. •
   A benchmark interest rate, from which other interest rates are calculated; a policy rate.

   • On loans to higher-risk customers, the bank charges 5% above the base rate.
2. •
   (UK) Especially, the interest rate at which the Bank of England lends money to commercial banks.
3. •
   The background rate of occurrence of any phenomenon, which informs any logical analysis of its rate of occurrence under any subset of circumstances; especially, the proportion of individuals in a population who have a certain characteristic (e.g., trait, experience, circumstance), irrespective of any treatment effects in a treatment group of a scientific study.