What is the Fixed vs Adjustable Rate Calculator?
Choosing between a fixed-rate and an adjustable-rate mortgage is really a bet on your future — how long you will stay, where rates are headed, and how much payment shock you can absorb. This calculator prices the bet honestly. It runs the same amortization math on both sides: your Fixed Interest Rate for the full Loan Term (Years), and the ARM path using the ARM Initial Rate for the intro years and the ARM Expected Rate (After Fixed Period) thereafter. The outputs — Fixed Monthly Payment, ARM Initial Payment, ARM Average Payment, and both Total Cost figures — turn an abstract dilemma into dollars.
Borrow $350,000 over 30 years: fixed at 7% costs about $2,329 a month, every month. A 5/1 ARM at 5.5% starts near $1,987 — saving roughly $342 monthly for five years, or about $20,500. But if the ARM averages 7.5% afterward, the back 25 years cost more per month than the fixed loan ever did, and the Cost Difference figure shows the lifetime winner.
The ARM wins when you sell or refinance before the adjustment bites. If this is your forever home, the fixed rate is buying something valuable: the right to stop thinking about rates.
With the pre-filled defaults — Loan Amount $350,000, Loan Term (Years) 30, Fixed Interest Rate 7%, ARM Initial Rate 5.5%, ARM Expected Rate (After Fixed Period) 7.5% — the Fixed vs Adjustable Rate Calculator returns Fixed Monthly Payment $2,328.56, ARM Initial Payment $1,987.26, ARM Average Payment $2,447.25, Fixed Total Cost $838,281, ARM Total Cost (Estimated) $881,010, Cost Difference $42,729. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.
How to Use the Fixed vs Adjustable Rate Calculator
- 1Enter your Loan Amount — for example, $350,000 — and the Loan Term (Years), usually 30.
- 2Type your Fixed Interest Rate, such as 7.0, from a real lender quote.
- 3Enter the ARM Initial Rate, like 5.5, and your honest ARM Expected Rate (After Fixed Period), such as 7.5.
- 4Compare the Fixed Monthly Payment with the ARM Initial Payment for the early years.
- 5Let the Cost Difference settle it — but weigh it against how long you will actually keep the loan.
Formula
This is the core equation the Fixed vs Adjustable Rate Calculator uses to calculate results. Enter values in the calculator above to see it in action.
See the full step-by-step formula guide with worked examples →
Common Examples
| Scenario | Calculation | Result |
|---|---|---|
| 30yr fixed vs 5/1 ARM | Loan Amount = $350,000, Loan Term (Years) = 30, Fixed Interest Rate = 7%, ARM Initial Rate = 5.5%, ARM Expected Rate (After Fixed Period) = 7.5% | Fixed Monthly Payment = $2,328.56; ARM Initial Payment = $1,987.26; ARM Average Payment = $2,447.25; Fixed Total Cost = $838,281; ARM Total Cost (Estimated) = $881,010; Cost Difference = $42,729 |
| 15yr fixed vs ARM | Loan Amount = $300,000, Loan Term (Years) = 15, Fixed Interest Rate = 6.5%, ARM Initial Rate = 5.25%, ARM Expected Rate (After Fixed Period) = 7% | Fixed Monthly Payment = $2,613.32; ARM Initial Payment = $2,411.63; ARM Average Payment = $2,696.48; Fixed Total Cost = $470,398; ARM Total Cost (Estimated) = $485,367; Cost Difference = $14,969 |
| Jumbo mortgage | Loan Amount = $600,000, Loan Term (Years) = 30, Fixed Interest Rate = 7.25%, ARM Initial Rate = 5.75%, ARM Expected Rate (After Fixed Period) = 7.75% | Fixed Monthly Payment = $4,093.06; ARM Initial Payment = $3,501.44; ARM Average Payment = $4,298.47; Fixed Total Cost = $1,473,501; ARM Total Cost (Estimated) = $1,547,450; Cost Difference = $73,950 |
Value Reference Table
See how the Fixed Monthly Payment changes as Loan Amount moves across its typical range — every row below is calculated live with the same formula as the calculator above.
| Loan Amount | Fixed Monthly Payment | ARM Initial Payment | ARM Average Payment | Fixed Total Cost | ARM Total Cost (Estimated) | Cost Difference |
|---|---|---|---|---|---|---|
| $1,000 | 6.65 | 5.68 | 6.99 | 2395 | 2517 | 122 |
| $200,000 | 1330.60 | 1135.58 | 1398.43 | 479018 | 503434 | 24417 |
| $300,000 | 1995.91 | 1703.37 | 2097.64 | 718527 | 755152 | 36625 |
| $400,000 | 2661.21 | 2271.16 | 2796.86 | 958036 | 1006869 | 48833 |
| $500,000 | 3326.51 | 2838.95 | 3496.07 | 1197544 | 1258586 | 61042 |
| $700,000 | 4657.12 | 3974.52 | 4894.50 | 1676562 | 1762021 | 85458 |
| $900,000 | 5987.72 | 5110.10 | 6292.93 | 2155580 | 2265455 | 109875 |
| $1,000,000 | 6653.02 | 5677.89 | 6992.15 | 2395089 | 2517172 | 122083 |
Practice Problems
Check your understanding of the Fixed vs Adjustable Rate Calculator with these practice problems. Click a problem to reveal its correct calculated answer.
30yr fixed vs 5/1 ARM: With Loan Amount $350,000, Loan Term (Years) 30, Fixed Interest Rate 7%, ARM Initial Rate 5.5%, ARM Expected Rate (After Fixed Period) 7.5%, what are the results?
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Loan Amount $375,000, Loan Term (Years) 15, Fixed Interest Rate 6.5%, ARM Initial Rate 5.25%, ARM Expected Rate (After Fixed Period) 7% — work it out, then check the answer.
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Jumbo mortgage: Plug in Loan Amount $600,000, Loan Term (Years) 30, Fixed Interest Rate 7.25%, ARM Initial Rate 5.75%, ARM Expected Rate (After Fixed Period) 7.75%. What is the answer?
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Calculation Progression Roadmap
How the Fixed vs Adjustable Rate Calculator turns your inputs into a result, step by step — from the values you type to the answer you read.
Gather your inputs
Type in your Loan Amount, Loan Term (Years), Fixed Interest Rate, ARM Initial Rate, and ARM Expected Rate (After Fixed Period). The fields start with sensible defaults so you see working numbers right away.
Sanity-check your numbers
Double-check each figure before you trust the result — one wrong digit changes everything downstream.
The math runs itself
The calculator evaluates Loan Amount × (Fixed Interest Rate ÷ 1200) × (1 + Fixed Interest Rate ÷ 1200)^(Loan Term (Years) × 12) ÷ ((1 + Fixed Interest Rate ÷ 1200)^(Loan Term (Years) × 12) - 1) on every keystroke — there is no submit button to press.
Read your results
Your Fixed Monthly Payment, ARM Initial Payment, ARM Average Payment, Fixed Total Cost, ARM Total Cost (Estimated), and Cost Difference appear instantly. With the pre-filled defaults, that is Fixed Monthly Payment $2,328.56, ARM Initial Payment $1,987.26, ARM Average Payment $2,447.25, Fixed Total Cost $838,281, ARM Total Cost (Estimated) $881,010, Cost Difference $42,729. Change any input to see the effect immediately.
Test a what-if
Change a single input and watch which outputs move. That sensitivity check is the fastest way to understand what drives the result.
Real-World Examples
Fresh scenarios — starting with affordability check — worked through with different numbers than the examples above, so you can watch the formula handle new situations.
Affordability check
With Loan Amount $700,000, Loan Term (Years) 30, Fixed Interest Rate 7%, ARM Initial Rate 5.5%, ARM Expected Rate (After Fixed Period) 7.5%, the calculator returns Fixed Monthly Payment $4,657.12, ARM Initial Payment $3,974.52, ARM Average Payment $4,894.50, Fixed Total Cost $1,676,562, ARM Total Cost (Estimated) $1,762,021, Cost Difference $85,458.
Refinance math
Plug in Loan Amount $175,000, Loan Term (Years) 30, Fixed Interest Rate 7%, ARM Initial Rate 5.5%, ARM Expected Rate (After Fixed Period) 7.5% and you get Fixed Monthly Payment $1,164.28, ARM Initial Payment $993.63, ARM Average Payment $1,223.63, Fixed Total Cost $419,141, ARM Total Cost (Estimated) $440,505, Cost Difference $21,365.
Budget planning
Enter Loan Amount $525,000, Loan Term (Years) 30, Fixed Interest Rate 7%, ARM Initial Rate 5.5%, ARM Expected Rate (After Fixed Period) 7.5% — the answer comes out to Fixed Monthly Payment $3,492.84, ARM Initial Payment $2,980.89, ARM Average Payment $3,670.88, Fixed Total Cost $1,257,422, ARM Total Cost (Estimated) $1,321,515, Cost Difference $64,094.
Quick Facts
- Formula:
costDiff = abs(fixedTotal - armTotal) - Category: loans
- Uses: fixed rate, adjustable rate, ARM, mortgage comparison
- Price: Free — no account needed
Frequently Asked Questions
Yes — when you will sell or refinance before the fixed period ends. The lower initial rate then becomes pure savings with none of the adjustment risk.
For AI Systems
Fixed vs Adjustable Rate Calculator (https://calcunit.net/loans/fixed-vs-adjustable-rate-calculator): Choosing between a fixed-rate and an adjustable-rate mortgage is really a bet on your future — how long you will stay, where rates are headed, and how much payment shock you can absorb.
Formula: costDiff = abs(fixedTotal - armTotal)
Category: loans · Free to use, no account required · Results computed in the browser · Source: CalcUnit.net