Interest Rate
Definition
The percentage you pay (on a loan) or earn (on savings) annually. If you borrow $1,000 at 5% interest rate, you pay $50 in interest per year. On savings, if a rate is 4%, you earn $40 yearly on a $1,000 balance. Expressed as APR or APY.
Why It Matters
Small interest rate differences compound into huge money over time. A 0.5% difference in mortgage rates costs tens of thousands over 30 years. A 1% higher savings rate can double your emergency fund earnings in a decade.
Example
Borrow $10,000 at 3% vs. 6% for 5 years. At 3%: you pay ~$796 interest. At 6%: you pay ~$1,637. That $3% difference costs you $841 on this one loan. Multiply across a mortgage and the difference is staggering.