A 30-year mortgage with a 6.5% rate on a $400,000 home doesn't mean much until you see the monthly number: $2,528. That single figure tells you whether the home fits your budget —or whether you need to keep looking.
What the Calculator Shows You
ToolKnit's mortgage calculator takes four inputs and produces a complete financial picture:
- Home Price — The total purchase price of the property
- Down Payment — Enter as a dollar amount or percentage (e.g. 20%)
- Loan Term — 15 or 30 years, with quick-toggle buttons
- Interest Rate — Annual rate from your lender's quote
Results update in real time as you adjust any slider or field. No “Calculate” button to click.
Understanding Your Results
Monthly Payment
This is the principal + interest you'll pay each month. It's the number your bank account cares about most. The calculator uses the standard amortization formula to compute this precisely.
Total Interest
Over 30 years, you often pay more in interest than the original loan amount. Seeing this total can be eye-opening —and it's the strongest argument for making extra payments or choosing a shorter term.
Payment Breakdown Chart
A visual donut chart splits your payment into principal vs. interest so you can see exactly where your money goes each month.
Amortization Schedule
A full year-by-year (or month-by-month) table showing how each payment chips away at the principal. Early payments are almost entirely interest; later ones are mostly principal. The schedule makes this shift crystal clear.
15-Year vs. 30-Year: Which Is Better?
There's no universal answer, but the calculator makes comparison easy:
- 30-year — Lower monthly payment, more total interest paid. Better for cash flow flexibility.
- 15-year — Higher monthly payment, dramatically less total interest. Better if you can afford it.
Toggle between the two terms and watch the numbers change. On a $300,000 loan at 6.5%, switching from 30 to 15 years saves you over $180,000 in total interest.
Tips for First-Time Buyers
- Aim for 20% down — It eliminates PMI (private mortgage insurance) and lowers your monthly payment significantly.
- Rate-shop aggressively — A 0.25% rate difference can mean $15,000+ over the life of the loan.
- Don't forget extras — Property tax, insurance, and HOA fees aren't included in the basic calculation but will affect your real monthly cost.
- Use the 28/36 rule — Housing costs shouldn't exceed 28% of gross income; total debt shouldn't exceed 36%.
Try it now: Open Mortgage Calculator — free, instant results, no sign-up required.