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Mortgage Refinance Calculator

Savings from refinancing. Free online Mortgage Refinance Calculator. Calculate mortgage refinance online — fast, accurate, mobile-friendly, no signup needed.

Principal, interest, taxes and insurance (PITI).
Monthly savings
$152.80

Derivation

  1. ├── 01Givenbal = 250000, old = 6.5, new_ = 5.5, years = 25
  2. ├── 02Formulat × (a / 1200) / (1-(1+a / 1200)^(12 × -r))-t × (n / 1200) / (1-(1+n / 1200)^(12 × -r))
  3. └── 03Compute Monthly savings$152.80
Did you know?

Making one extra mortgage payment per year cuts a 30-year loan by ~4 years on average.

§01What is

Understanding the Mortgage Refinance Calculator

The Mortgage Refinance Calculator computes Monthly savings from 4 inputs: remaining balance ($), old rate (%), new rate (%), years left. Savings from refinancing.

Quick calculators for the math that shouldn’t need a notepad — instant, accurate, private to your browser. The Mortgage Refinance Calculator sits in that toolkit — it savings from refinancing. Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

t × (a / 1200) / (1-(1+a / 1200)^(12 × -r))-t × (n / 1200) / (1-(1+n / 1200)^(12 × -r))

Where

bal
Remaining balance ($)
old
Old rate (%)
new_
New rate (%)
years
Years left
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: Remaining balance ($) = 250000, Old rate (%) = 6.5, New rate (%) = 5.5, Years left = 25.

  1. 01Start by noting the input — Remaining balance ($): 250000.
  2. 02Start by noting the input — Old rate (%): 6.5.
  3. 03Start by noting the input — New rate (%): 5.5.
  4. 04Start by noting the input — Years left: 25.
  5. 05Substitute these values into the formula: t × (a / 1200) / (1-(1+a / 1200)^(12 × -r))-t × (n / 1200) / (1-(1+n / 1200)^(12 × -r))
  6. 06Compute Monthly savings: the calculator returns 152.799.
  7. 07Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Mortgage Refinance Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

Remaining balance ($) halved

bal = 125000 (from 250000)

Keep every other input at its default and halve the remaining balance ($). See how monthly savings responds.

  1. 01New Remaining balance ($): 125000
  2. 02Baseline Monthly savings: 152.799
  3. 03New Monthly savings: 76.3996
  4. 04Monthly savings decreases by 50% → use this sensitivity to plan for real-world variation.
02 · PATTERN

Remaining balance ($) doubled

bal = 500000 (from 250000)

Keep every other input at its default and double the remaining balance ($). See how monthly savings responds.

  1. 01New Remaining balance ($): 500000
  2. 02Baseline Monthly savings: 152.799
  3. 03New Monthly savings: 305.598
  4. 04Monthly savings increases by 100% → use this sensitivity to plan for real-world variation.
03 · PATTERN

Old rate (%) halved

old = 3.25 (from 6.5)

Keep every other input at its default and halve the old rate (%). See how monthly savings responds.

  1. 01New Old rate (%): 3.25
  2. 02Baseline Monthly savings: 152.799
  3. 03New Monthly savings: -316.928
  4. 04Monthly savings decreases by 307.4% → use this sensitivity to plan for real-world variation.
04 · PATTERN

Old rate (%) doubled

old = 13 (from 6.5)

Keep every other input at its default and double the old rate (%). See how monthly savings responds.

  1. 01New Old rate (%): 13
  2. 02Baseline Monthly savings: 152.799
  3. 03New Monthly savings: 1284.37
  4. 04Monthly savings increases by 740.6% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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