What happens if my rate lock expires before closing?

If your lock expires before closing, you can extend it — most lenders charge 0.125–0.375% of the loan amount — or re-lock at current market rates. To avoid this, choose a lock period covering your expected closing date plus a 7–10 day buffer.

What is a float-down option on a rate lock?

A float-down option lets you renegotiate your locked rate downward one time if market rates drop more than a threshold after locking. It typically costs 0.25–0.50% of the loan upfront. You're protected if rates rise but can still capture a meaningful drop.

How much does it cost to buy down a mortgage rate?

Discount points cost 1% of the loan amount per point and typically reduce the rate by 0.25% per point. The break-even period is usually 4–7 years. Buying points makes sense if you plan to keep the loan past break-even.

Mortgage Rate Lock Calculator

Should you lock your mortgage rate now or float and wait? Compare all rate scenarios, see what a 0.25–0.50% move costs you, and use 5+ years of historical volatility data to make a confident decision.

Loan Amount

Rate Offered

Lock Period

Rate Trend Expectation

Loan Term

Lock Cost (points)

pts

Monthly Payment at Locked Rate

$2,270/mo

Recommendation: Lock now — rates expected flat, locking eliminates risk

Monthly Payment (current rate)

$2,270

Lock Cost

Free

Extra cost if rates rise 0.25%

$58/mo

Extra cost if rates rise 0.50%

$118/mo

Annual risk exposure (+0.25%)

$702/yr

Annual risk exposure (+0.50%)

$1,410/yr

Advanced

Float vs Lock Deep Dive

Full scenario comparison across all rate outcomes plus lock period cost differences

What happens to your payment and total cost under each rate scenario — locked at 6.75% vs floating:

Rates Drop 0.50%

$2,155/mo

Rate: 6.25%

Save $115/mo floating

Save $41,430 total

Rates Drop 0.25%

$2,212/mo

Rate: 6.50%

Save $58/mo floating

Minus: lock cost $0

Rates Stay Flat (Lock = Safe)

$2,270/mo

Rate: 6.75%

Locked rate = same outcome

Lock cost: $0

Rates Rise 0.25%

$2,329/mo

Rate: 7.00%

Floating costs $58/mo more

Extra over loan: $21,048

Rates Rise 0.50%

$2,388/mo

Rate: 7.25%

Floating costs $118/mo more

Extra over loan: $42,309

With rates expected flat, locking eliminates uncertainty. Your locked payment of $2,270/mo is guaranteed regardless of market moves.

Pro

Historical Volatility & Extended Lock Analysis

Rate move probabilities based on 2020–2026 data, builder locks, and float-down renegotiation

Based on US 30-year fixed mortgage rate monthly changes from January 2020 to mid-2025:

Monthly Std Deviation

0.28%

Average monthly rate swing

Average Monthly Change

+0.044%

Direction bias 2020–2025

P(+0.25% in 30 days)

80%

Probability rates rise ≥0.25%

P(+0.25% in 60 days)

71%

P(+0.25% in 90 days)

67%

Total Months Analyzed

Jan 2020 – mid 2025

Rate change distribution (monthly):

Drop > 0.50%

2 of 67 (3%)

Drop 0.25–0.50%

4 of 67 (6%)

Change < 0.25%

45 of 67 (67%)

Rise 0.25–0.50%

11 of 67 (16%)

Rise > 0.50%

5 of 67 (7%)

How to Use This Mortgage Rate Lock Calculator

Enter your Loan Amount, the Rate Offered by your lender, and select your desired Lock Period (30, 45, 60, or 90 days). Choose your Rate Trend Expectation — whether you expect rates to rise, stay flat, or fall — and the calculator shows your locked payment, cost of the lock, and financial risk if you float instead.

The Advanced tier compares all five rate scenarios side by side. The Pro tier uses 2020–2025 historical volatility data to estimate the probability of a rate move of 0.25% or more within your lock window.

Rate Lock Cost Formulas

Monthly Payment = Loan × [r(1+r)^n] / [(1+r)^n − 1]
Lock Cost ($) = Lock Points × Loan Amount / 100
Risk Exposure (0.25% rise) = [Payment(rate+0.25%) − Payment(rate)] × Loan Term months
Break-Even (buydown) = Point Cost / Monthly Savings from lower rate

Example: 30-Day Lock vs Floating on $350,000 Loan

Rate offered: 6.75% | Lock period: 30 days | Loan term: 30 years

Monthly Payment (locked at 6.75%)	$2,270/mo
Lock cost	$0 (free 30-day lock)
If rates rise to 7.00% (floating)	$2,329/mo (+$59/mo)
Extra cost over 30-year loan	$21,240
If rates drop to 6.50% (floating)	$2,212/mo (save $58/mo)
Savings over 30-year loan	$20,880
1-point buydown cost	$3,500
Break-even on buydown	~60 months (5 years)

Locking protects against the $21,240 upside risk. Floating offers potential $20,880 savings but requires correctly predicting rate direction — which even professional economists frequently get wrong.

Frequently Asked Questions

A mortgage rate lock is a lender's guarantee to hold your interest rate for a set period — typically 30, 45, 60, or 90 days — while your loan processes. If market rates rise before closing, your locked rate is protected. If rates fall, you generally don't benefit unless you have a float-down option. Rate locks give you certainty over your future mortgage payment.

Lock when you have an accepted offer and are confident in your closing timeline. If rates are trending upward or you expect volatility, locking sooner protects you. If rates are falling steadily, floating briefly may save money — but carries real risk. Most financial advisors recommend locking unless you have strong conviction rates will drop, since missing a closing deadline with an expired lock can be costly.

If your lock expires before closing, you typically have two options: (1) extend the lock — most lenders charge an extension fee of 0.125–0.375% of the loan amount or about $15–25 per day, or (2) re-lock at current market rates, which could be higher or lower. To avoid this, choose a lock period that covers your expected closing date plus a 7–10 day buffer for unexpected delays.

A float-down option lets you renegotiate your locked rate downward one time if market rates drop more than a threshold (usually 0.25–0.50%) after locking. The option typically costs 0.25–0.50% of the loan upfront. It's a good choice in uncertain rate environments — you're protected if rates rise but can still capture a meaningful drop. Read the fine print: most float-downs have a specific exercise window, often 5–10 business days before closing.

Discount points cost 1% of the loan amount per point and typically reduce the rate by 0.25% per point, though this varies by lender. The break-even period — when accumulated monthly savings exceed the upfront cost — is usually 4–7 years. Buying points makes sense if you plan to keep the loan past break-even and rates are stable. If you might refinance or sell within a few years, skip the points.