Free Mortgage Calculator: Crush Your Home Loan in 2026
Here's the most expensive number in your life.
Your mortgage interest.
For a $400,000 home with a 30-year fixed at 7%, you'll pay roughly $560,000 in interest alone. On a $400k loan. That's not a typo.
But here's the kicker: small tweaks — a 15-year term, an extra $200/month, refinancing at the right time — can save you $100,000+ in interest. Easily.
In this guide, I'll show you the free mortgage calculator I used to save $74,000 on my own home loan, plus a step-by-step strategy for crushing your mortgage faster.
Why most mortgage calculators are useless#
Most "free mortgage calculators" online give you one number: monthly payment.
That's not enough.
You need:
- Total interest paid over the life of the loan
- Amortization schedule (how much of each payment goes to principal vs interest)
- What happens with extra payments
- Refinance break-even analysis
- Comparison between 15-year and 30-year terms
Without those, you're just buying a number.
The mortgage calculator I use#
All five features above. Plus comparison tables for different rates, terms, and prepayment strategies.
Free. No signup. Runs in your browser.
Step-by-step: planning your mortgage#
Let me walk through a real scenario.
Step 1: Get clear on the numbers#
You need:
- Loan amount (home price minus down payment)
- Interest rate (current 30-year fixed is ~7%; check today's rates)
- Term (15 or 30 years; sometimes 20)
- Property tax (annual; usually 1-2% of home value)
- Home insurance (annual; ~$1,200-3,000)
- HOA fees (if applicable)
Many calculators only do the first three. PITI (Principal, Interest, Taxes, Insurance) is what you actually pay monthly.
Step 2: Run the base scenario#
Plug in your numbers. Note:
- Monthly payment
- Total interest over the life of the loan
- Total cost (principal + interest)
Brace yourself for the total interest number. It's always shocking on a first-time mortgage.
Step 3: Run the 15-year version#
Same loan amount, 15-year term, slightly higher monthly payment.
For my house, the difference was:
- 30-year at 7%: $2,660/mo, $558k total interest
- 15-year at 6.5%: $3,485/mo, $227k total interest
The 15-year costs $825/mo more but saves $331,000 in interest.
If your budget can swing it, 15-year is the wealth-building choice.
Step 4: Try extra payments#
Even on a 30-year, adding extra principal each month accelerates payoff dramatically.
$200/month extra on a $400k mortgage at 7%:
- Saves ~$130,000 in interest
- Pays off 7 years earlier
That's a 36% return on those extra dollars, in interest savings.
Step 5: Check refinance scenarios#
If rates drop or your credit improves, you can refinance.
Rule of thumb: refinance saves money when:
- New rate is 0.75-1% lower than current
- You'll stay in the home long enough to recoup closing costs (usually 2-3 years)
Run the break-even in your calculator. Look at "months to break-even." If you'll be in the house longer than that, refinance.
Step 6: Compare lenders#
Don't take the first offer.
Get rate quotes from 3-5 lenders. Even a 0.25% difference matters over 30 years:
- 7.00% vs 6.75% on $400k: $32,000 over 30 years
Lenders compete. Use that.
How the math works (briefly)#
Monthly payment formula:
M = P × [r(1+r)^n] / [(1+r)^n - 1]
Where:
- M = monthly payment
- P = principal (loan amount)
- r = monthly interest rate (annual rate / 12)
- n = total months (years × 12)
In English: each monthly payment covers some interest and some principal. Early in the loan, most of your payment is interest. Later, it flips to mostly principal.
That's why extra principal payments are so powerful — they shrink the balance, which shrinks future interest, which compounds.
Real example: my $74k savings#
Here's my actual situation when I bought my house.
Original loan: $350,000 at 6.875% on a 30-year.
Monthly payment: $2,299.
Total interest over 30 years: $477,640.
I ran the mortgage calculator and tried:
Option A: Stay with the original loan. Pay normally.
- Total interest: $477,640.
Option B: Pay an extra $300/month.
- Total interest: $325,000.
- Payoff: 7 years earlier.
Option C: Refinance to 15-year when rates dropped to 5.5%.
- Total interest: $158,000.
- Payoff: 15 years total.
I went with Option C two years in. Saved $74,000+ vs my original trajectory, will be mortgage-free 13 years sooner.
That decision came from 20 minutes with a calculator.
Common mortgage mistakes#
After watching friends buy homes:
Mistake 1: Buying the maximum you qualify for. Just because the bank approves $600k doesn't mean you should borrow it. Aim for 25% of gross income on PITI, max.
Mistake 2: Skipping the down payment. Less than 20% down means PMI (private mortgage insurance) — extra $200-400/month for nothing.
Mistake 3: Choosing 30-year by default. If you can afford 15-year, the lifetime savings are massive.
Mistake 4: Not paying extra principal. Even $50/month extra compounds dramatically.
Mistake 5: Refinancing too often. Each refi has closing costs ($3,000-8,000). Only refi when savings justify the cost.
ARM vs Fixed#
Quick note on adjustable-rate mortgages.
ARMs start at a lower rate (e.g., 5.5% vs 7% fixed) but the rate adjusts after 5, 7, or 10 years.
Use an ARM if:
- You'll definitely sell or refinance before the adjustment
- You can stomach the risk if rates rise
Otherwise, fixed-rate is the default for most buyers. Predictability is worth the slightly higher rate.
Pro tips#
Quick wins:
Tip 1: Always include PITI, not just principal+interest. The full picture is what hits your bank account.
Tip 2: Use the amortization schedule. See exactly when your loan flips from interest-heavy to principal-heavy.
Tip 3: Round up your monthly payment. Even $25 extra/month makes a difference.
Tip 4: Apply tax refunds and bonuses to principal. Lump sum extra payments are huge.
Tip 5: Check if your lender allows recasting. Lump sum + recast = lower monthly payment, same term.
What about renting vs buying?#
The eternal debate.
A rent vs buy calculator factors in:
- Mortgage payment + property tax + insurance + maintenance
- vs rent + investment returns on the down payment you'd otherwise invest
For short-term moves (under 5 years), renting usually wins.
For long-term (10+ years in one place), buying often wins.
Run the numbers. Don't assume.
Wrap-up#
Your mortgage will likely be the largest debt you ever take on.
Spend 30 minutes with a free mortgage calculator before you sign anything.
Molixa Mortgage Calculator has everything you need.
The decisions you make in those 30 minutes can save you tens of thousands.
Don't wing it.
Catch you on the next one.