How Much Interest Will You Really Pay?
Monthly payments make loans feel manageable. The lifetime interest cost tells a very different story. This guide shows the true total cost of common loans — sometimes more than the original amount borrowed.
Quick answer
On a $300K mortgage at 6.5% over 30 years, you pay back ~$682,000. A $25K car loan at 8% costs ~$30,400. A $5K credit card balance at 24%, paying minimums, can cost $11,000+ over 15+ years.
Mortgage: the biggest interest bill of your life
- $300K @ 6.5%, 30-yr: pay $1,896/mo × 360 = $682,560 total. Interest: ~$382,560.
- $300K @ 6.5%, 15-yr: pay $2,613/mo × 180 = $470,340 total. Interest: ~$170,340 (saves $212K).
- $300K @ 5.5%, 30-yr: pay $1,703/mo × 360 = $613,080 total. Interest: ~$313,080.
Even a 1% rate change saves over $70K. Term length matters even more — the 15-year saves over $200K despite a higher monthly payment.
Car loans
- $25K @ 8%, 5-yr: $507/mo, total $30,415. Interest: $5,415.
- $25K @ 8%, 7-yr: $390/mo, total $32,734. Interest: $7,734.
- $50K @ 8%, 7-yr: $779/mo, total $65,468. Interest: $15,468.
Longer car loans look cheaper monthly but cost much more — and you owe more than the car is worth for years.
Credit cards (the most expensive)
- $5,000 @ 24%, paying $125/min: 6+ years, ~$3,800 interest.
- $5,000 @ 24%, paying minimum 2%: 15+ years, ~$11,000+ interest.
- $5,000 @ 24%, paying $300/mo: ~20 months, ~$1,140 interest.
Minimum payments are a trap. Doubling or tripling them cuts the interest cost by 60–90%.
Student loans
- $30K @ 6%, 10-yr standard: $333/mo, total $39,966. Interest: $9,966.
- $30K @ 6%, 25-yr extended: $193/mo, total $57,961. Interest: $27,961.
Income-driven repayment plans can ease cash flow but often increase total interest paid significantly.
Use the calculator
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Frequently Asked Questions
Why is the total so much higher than I expect?
Compounding works against you when you owe money. Interest accrues on the outstanding balance — and on early payments, most of what you pay just covers that interest.
How can I reduce total interest?
Higher monthly payments, shorter term, lower rate (refinance if you can), and avoiding extending the loan.
Does paying extra at the start save more than at the end?
Yes — early extra payments reduce more future interest. The first few years of a long loan are the highest-leverage time to add extra.
Are 0% loans really 0%?
Often yes for the promo period — but watch for retroactive interest if not paid in full by the deadline. Read the fine print.