Can I Afford to Move? Low-Rate Mortgage Calculator for Charleston, SC

A worked example

Here’s the math for a made-up but realistic family: they own a $650,000 home with a 3% loan and want an $850,000 home in Carolina Park in Mount Pleasant. The selling costs, closing costs, insurance and HOA figures are example numbers, not quotes. The property tax uses Carolina Park’s 2026 millage at the 4% ratio, and the rate is the November 5, 2026 national average.

Worked example: moving up from a 3% mortgage
Step	Example
Sale price of current home	$650,000
Mortgage payoff	−$310,000
Cost to sell (example)	−$45,000
1. Walk away with	$295,000
Kept back for moving and emergencies	−$25,000
Buyer closing costs (example)	−$17,000
Down payment on the next home	$253,000 (30%)
Loan amount	$597,000
Principal and interest, 30-year fixed at 7.18%	$4,044
Property tax, Carolina Park at 4% ($3,037 a year)	$253
Homeowners insurance (example, $3,600 a year)	$300
HOA (example)	$90
2. New monthly payment	$4,687
What they pay now, all in	−$2,150
3. Real difference	+$2,537 a month

They’d told themselves $1,500 more a month was their limit. At this price and rate they’re $1,037 over. A rate one point lower would bring the difference to about $2,142, still over. So for them the honest answer is not this house, not yet: a lower price, a builder buydown, or waiting would have to close the gap. Notice the property tax isn’t what breaks it here. It’s the rate on a bigger loan. That’s different for every family, which is why you run your own numbers.

Why the rate isn’t the whole story

On a 30-year fixed loan, every $100,000 borrowed costs about $422 a month in principal and interest at 3%, and about $677 at 7.18%. That gap is real. But you won’t borrow the same amount on the same house. If you’ve built up equity, a big down payment shrinks the new loan. If you’re moving to something smaller or less expensive, the new payment can come out close to what you pay now, even at a higher rate. The only way to know is to work the three numbers.

The Charleston part: your new tax bill

South Carolina limits how much your home’s taxable value can go up at each countywide reassessment: 15%, even if the market value rose more. If you’ve owned your home through a reassessment or two, you’re likely being taxed on less than it’s worth.

When you buy, that protection doesn’t come with you. A sale is an assessable transfer of interest, and the county revalues the home you buy at a current value. You also have to apply for the 4% legal residence ratio on the new home; it doesn’t carry over automatically. Until you do, you’re billed at 6%. The good news: a legal residence at 4% is exempt from school operating millage, so a primary home’s bill is far smaller than a second home’s. The 4% vs 6% estimator shows the difference.

Ways to change the math

A seller- or builder-paid rate buydown

A seller or builder can pay points to lower your rate, either for the life of the loan or for the first few years. There are limits. On a conventional loan for a home you’ll live in, Fannie Mae caps these contributions at 3% of the price with less than 10% down, 6% with 10% to 25% down, and 9% with more than 25% down. Move-up buyers often have a large down payment, which means more room to negotiate a buydown. The lever table above shows what a lower rate would do to your difference.

New construction incentives

Builders around Charleston often offer closing cost help or rate incentives through their preferred lender, and they change often. Compare the incentive with what an outside lender quotes you. Here are the communities selling new homes right now.

An assumable loan

FHA and VA loans can be assumed with the loan holder’s approval, and you keep the seller’s rate. You need cash (or a second loan) for the gap between the price and the balance, and approval can take a while. They’re not common, but when one fits, it can change everything.

A different price, or more down

If you set a comfort number above, the lever table shows the price that fits it and how much more cash down it would take at the price you entered. Sometimes the answer is a different neighborhood, not a different decision.

Sell first, buy first, or both at once

Most move-up buyers need the equity from the sale to buy the next house. That can mean a contingent offer, a rent-back after closing, or bridge financing. Each has costs and risks, and it’s worth a plan before you list. Talk to a lender about what you qualify for while you still own your current home.

When the honest answer is “not yet”

If the difference is more than you’re comfortable with, or your equity doesn’t cover the costs to sell and buy, waiting is a perfectly good decision. Keep paying down the 3% loan, let your equity build, and run the numbers again when rates, prices or your plans change. I’d rather you stay put than stretch into a payment that makes the new house stressful.

Common questions

Should I give up my 3% mortgage rate to move?

Only if the house is worth the difference to you, and you can carry it. Work out three numbers: what you’d walk away with after selling, what the new payment would be, and how much more that is per month than you pay now. If the monthly difference is a number you’re comfortable with for the life you’d get, the low rate shouldn’t be what keeps you. If it isn’t, the honest answer is “not yet,” and that’s a fine answer.

How much more is a 7% mortgage than a 3% mortgage?

On a 30-year fixed loan, principal and interest on every $100,000 borrowed is about $422 a month at 3% and about $677 a month at 7.18% (the national average for the week of November 5, 2026, per Freddie Mac). Taxes, insurance and HOA dues come on top. Because you’re usually borrowing a different amount on a different house, the real difference has to be worked out with your numbers.

Will my property taxes go up if I buy a different house in Charleston?

Probably. South Carolina limits how much your home’s taxable value can rise at each countywide reassessment (the 15% cap), so long-time owners are often taxed on less than market value. A sale is an "assessable transfer of interest," and the county revalues the home you buy at a current value. You also have to apply for the 4% legal residence ratio on the new home; it doesn’t carry over. Don’t use the seller’s tax bill to estimate yours.

Can a seller or builder pay to buy down my interest rate?

Often, yes, within limits. On conventional loans, Fannie Mae caps what a seller, builder or other interested party can contribute toward your financing costs: 3% of the price if you put less than 10% down, 6% with 10% to 25% down, and 9% with more than 25% down, for a home you’ll live in. Ask your lender how a buydown would be structured and what it would do to your payment.

Can I buy a house with an assumable low-rate mortgage?

Sometimes. FHA and VA loans can be assumed if the loan holder approves you, and you keep the seller’s rate. The catch is cash: you have to cover the gap between the price and the loan balance, and approval and processing can take time. For VA loans, sellers also care about getting released from liability and what happens to their entitlement.

Will I owe tax when I sell my house?

Many owners won’t. If you owned and lived in the home as your main home for at least two of the last five years, you can generally exclude up to $250,000 of gain, or $500,000 if married filing jointly. Gain above that can be taxable. Talk to your tax advisor before you list.

Sources

Rates, rules and millage checked November 8, 2026. Mortgage rates change weekly.

Can I afford to move if I have a 3% mortgage?

Your move-up worksheet

Your three numbers

What would change the math