David Chen is a Certified Financial Analyst with over 10 years of experience in adjustable-rate mortgage products and interest-rate risk modelling.
Use this free 3 year ARM mortgage calculator to estimate your initial monthly payment, worst-case adjustment, and total interest over the life of the loan.
3 Year ARM Mortgage Calculator
3-Year ARM Formula
Initial Payment: M = P × [ r(1+r)^n ] / [ (1+r)^n – 1 ]
Adjusted Rate: min(Initial + LifetimeCap, max(Index+Margin, Initial + PeriodicCap))
Formula Sources: Investopedia | CFPB
Variables
- Initial Rate: Fixed rate for first 36 months.
- Periodic Cap: Max increase/decrease at each adjustment.
- Lifetime Cap: Max increase over life of loan.
- Index+Margin: Fully-indexed rate after first reset.
Related Calculators
- 5 Year ARM Mortgage Calculator
- 7 Year ARM Mortgage Calculator
- Interest-Only ARM Calculator
- ARM vs Fixed Mortgage Calculator
What Is a 3 Year ARM Mortgage?
A 3-year adjustable-rate mortgage (ARM) locks an initial interest rate for 36 months, then adjusts annually based on a benchmark index plus a set margin. Caps limit how much the rate can change at each reset and over the life of the loan.
How to Calculate 3 Year ARM (Example)
- Enter the loan amount (e.g., $400,000).
- Input the introductory rate (e.g., 4.5%).
- Set periodic cap (e.g., 2%) and lifetime cap (e.g., 5%).
- Enter the expected fully-indexed rate (index + margin, e.g., 6.5%).
- Click “Calculate” to see initial payment, adjusted payment, and total interest.
Frequently Asked Questions (FAQ)
How often does the rate adjust after year 3? Once every 12 months unless your note specifies otherwise.
Can the rate go down? Yes, if the index drops—subject to the periodic cap.
What is the worst-case payment? The calculator shows the payment at the lifetime cap; budget for that level.
Is a 3-year ARM better than a 5-year ARM? It depends on how long you plan to stay; break-even analysis is key.