Finance category

Mortgage, loan, investing, tax, and money calculators.

Mortgage Rate Lock Calculator

Compare your locked mortgage rate against where the market sits now. Include any lock extension fee to see the true net savings or cost from locking when you did.

Loan amount

Term (years)

Locked rate

If you'd floated, current rate

Lock extension fee per 30 days

Extension days needed

Net savings from lock

$24,177

over the life of the loan

Locked payment

$2,628

6.875%

Floated payment

$2,695

+$67/mo over locked

Extension cost

if 0-day extension needed

Reading the number

Locking saved money — even after extension fees, the locked rate is cheaper than what you'd be paying by floating.

Lock decisions trade certainty for cost. A 30-day lock is usually free; longer locks (45/60/90 days) and extensions cost real money. Match the lock period to your expected close date with a small buffer.

Editorial noteMaintained by EveryCalc - Reviewed June 2026

EveryCalc calculators are designed for fast, practical estimates with transparent inputs and no required account. We use plain formulas, visible assumptions, and related tools so visitors can check the result from more than one angle.

Results are informational only. For financial, tax, legal, medical, construction, or other high-impact decisions, verify the output against primary sources or a qualified professional.

Learn more about our review process on the EveryCalc methodology page.

How this calculator works

What this page estimates

This Mortgage Rate Lock Calculator is built to give a quick, browser-based estimate for mortgage rate lock. Compare your locked mortgage rate against where the market sits now. Include any lock extension fee to see the true net savings or cost from locking when you did. The inputs stay on the page during normal use, and the result should be treated as an estimate for planning, comparison, or education rather than professional advice.

Calculation approach

The calculator applies the standard relationship implied by the inputs, then formats the answer so it can be checked and reused. For finance tools, the most important step is using consistent units, rates, time periods, and assumptions before comparing the result with another calculator or outside quote.

Example workflow

For example, start with a realistic value you already know, change one input at a time, and watch how the answer moves. That makes it easier to tell whether the result is being driven by the main amount, the rate, the time period, or a unit conversion.

Practical checks

Use current, real-world numbers when the result affects money, health, tax, or legal decisions.
Run a low, base, and high case when the inputs are estimates.
Check the related calculators below when the next decision depends on a different assumption.

How to interpret the mortgage rate lock result

Best use

Use the result as a planning number for comparing payments, rates, returns, tax reserves, or cash-flow choices before you request a quote or make a commitment.

Cross-check

Compare the answer with the contract, lender estimate, tax form, brokerage statement, payroll record, or invoice that will control the real-world outcome.

Watch for

Do not rely on a single optimistic rate, return, or fee assumption. Money pages work best when you run low, base, and high cases and keep professional advice separate from the estimate.

This page belongs to the Finance calculator library, so the answer should be read in the context of the decision you are modeling rather than as a universal rule.

Before relying on this mortgage rate lock estimate

Most calculator mistakes come from the inputs, not the arithmetic. Use this short audit before you reuse the answer in a spreadsheet, quote, application, or important conversation.

Confirm source numbers

Match balances, rates, fees, taxes, income, and payment dates against the lender quote, payroll record, tax form, statement, invoice, or contract.

Separate cash flow from total cost

A lower monthly payment can still cost more over time if fees, interest, taxes, or a longer term are hidden in the structure.

Run conservative cases

Test at least one higher-cost or lower-return case before using the output for a purchase, refinance, investment, loan, or tax decision.

Rerun this page when the rate, price, term, fee, tax rule, income, expense, or expected holding period changes.

How to Use

Enter the loan amount and term.
Enter the rate you locked.
Enter today's available rate (or what your lender would offer if you re-locked).
If you needed to extend the lock, enter the extension fee per 30 days and the days extended.
Read the net savings or cost over the life of the loan.

Frequently Asked Questions

How long do lock periods last?

Standard locks run 30, 45, or 60 days. Longer locks (75/90/120 days) cost more upfront. Most refinances close inside 30 days; new construction may need a long lock or a float-down option.

What's a float-down option?

A feature on some locks that lets you re-lock at a lower rate one time before close, usually for a fee or rate adjustment. Useful when you're worried about rate volatility but want upside if rates drop.

What does a lock extension cost?

Typically 0.125–0.25% of loan amount per 15–30 days of extension. On a $400k loan that's $500–$1,000 per extension. Plan close dates carefully to avoid extensions.

Can I cancel a lock if rates drop?

Sometimes — but it usually means walking away from the lender or paying a re-lock fee. Some lenders offer one free float-down. Most do not let you cancel and re-lock for free.