Buy Sell Mortgage Calculator
Moving house chains two transactions together: the sale that frees your equity, and the purchase that consumes it. This buy sell mortgage calculator runs the chain in one pass. Enter your current home’s value and mortgage balance, your selling costs, and the price, down payment, rate and term of the next home, and it returns your net sale proceeds, the new loan and monthly payment, the cash you need at closing, and a plain feasibility verdict: does the sale fund the move, or is there a shortfall to cover?
It is not a first-time buyer affordability tool, and it does not assume a loan. It plans a sale and a purchase that depend on each other, which is the situation most movers are actually in.
The new payment covers principal and interest only. Your real monthly outlay will also include property taxes, homeowners insurance, and any HOA dues, so add those when you budget. Selling costs and down payment percentages left blank use the tool’s defaults (8% and 20%); entering 0 does the same, because the tool treats 0 as “not set” for those two fields.
Quick Answer
Key takeaways
- Equity is not proceeds. Selling costs come out first: at 7% on $450,000, that is $31,500 gone before the down payment sees a dollar.
- The verdict compares net proceeds with cash needed at closing (down payment plus closing plus moving costs). A positive surplus means the sale funds the move; a negative one is the extra cash you must find.
- A surplus can grow while the plan gets worse. A cheaper down payment percentage raises the surplus and the monthly payment at the same time, as the second scenario below shows.
- The bridge loan toggle annotates the verdict; it does not price bridge interest. Buying before you sell costs more than this tool shows.
- Quick Answer
- How the buy-sell math works, in three steps
- Worked example: selling a $450,000 home to buy a $500,000 home
- The surplus that lies: a bigger home at 20 percent down
- Selling costs, defaults, and the fields that treat zero as blank
- Buy first or sell first
- What other buy-sell tools miss
- Frequently Asked Questions
- Add This Calculator to Your Website
- References
How the buy-sell math works, in three steps
The sell side. Equity = home value – mortgage balance. Net sale proceeds = equity minus selling costs, where selling costs are your percentage applied to the sale price. On the worked example: $450,000 – $220,000 – $31,500 = $198,500.
The buy side. Down payment = your percentage of the new price; new loan = price – down payment; the new monthly payment uses the standard amortization formula on that loan, principal and interest only.
The feasibility check. Cash needed at closing = down payment + new home closing costs + moving costs. Surplus = net proceeds – cash needed. Positive means Feasible; negative means Additional Cash Required, and the size of the negative is the cash gap.
Worked example: selling a $450,000 home to buy a $500,000 home
The calculator is pre-filled with this case: $450,000 current value, $220,000 balance, 7% selling costs, a $500,000 target at 30% down, 6% over 30 years, a current payment of $1,800, $5,000 of moving costs, $12,000 of closing costs, and no bridge loan. Every figure below is the tool’s output.
| Output | Value |
|---|---|
| Current home equity | 230,000.00 |
| Net sale proceeds | 198,500.00 |
| Down payment required (30%) | 150,000.00 |
| New loan amount | 350,000.00 |
| New monthly payment (P and I) | 2,098.43 |
| Payment difference vs current $1,800 | 298.43 |
| Total transaction costs | 48,500.00 |
| Cash needed at closing | 167,000.00 |
| Surplus | 31,500.00 |
| Annual payment change | 3,581.12 |
| New home LTV | 70.00% |
| Equity position change | -80,000.00 |
| Feasibility verdict | Feasible |
That equity position change deserves a pause. The move is feasible, yet the stake line drops by $80,000 on day one. The gap decomposes exactly: $31,500 went to selling costs, $17,000 to closing and moving costs, and $31,500 is still yours, as the surplus cash. The tool’s equity line counts only the stake in the new home, not cash in hand, which is why it falls by more than the move actually cost ($48,500 in total transaction costs). Feasible means fundable, not free. If the next home also has to pass an income test, and most do, run it through the buy a home calculator as well: this tool checks your cash, that one checks your ratios.
The surplus that lies: a bigger home at 20 percent down
Change two inputs: the target price rises to $650,000 and the down payment drops to 20%. The tool now reports proceeds of $198,500.00 against cash needed of $147,000.00, a surplus of $51,500.00, and a Feasible verdict. The surplus grew by $20,000. So did the obligation: the new loan is $520,000, the payment is $3,117.66, and the payment difference is $1,317.66 a month, forever, against $298.43 in the first plan.
| Plan | Surplus | New payment | Monthly increase |
|---|---|---|---|
| $500,000 home, 30% down | $31,500.00 | $2,098.43 | +$298.43 |
| $650,000 home, 20% down | $51,500.00 | $3,117.66 | +$1,317.66 |
The verdict answers “can the sale fund the closing”, not “can the household fund the payment”. Before you celebrate a surplus, check the new payment against your income ratios with the affordability ratio calculator, and remember this tool’s payment excludes taxes, insurance and HOA dues, which rise with the price too.
Selling costs, defaults, and the fields that treat zero as blank
Selling costs usually total 7 to 10 percent of the sale price: roughly 5 to 6 percent in agent commissions plus 1 to 3 percent in seller closing costs, transfer taxes and fees. Guidance for sellers, such as the Veterans United home sale proceeds guide, puts total seller costs including commissions in the same 8 to 10 percent band. Enter your real combined percentage from your listing agreement where you have one.
Two fields have defaults you should know about. Leave selling costs blank, or enter 0, and the tool uses 8%. Leave the down payment percentage blank, or enter 0, and it uses 20%. The term defaults to 30 years the same way. That design means you cannot model a genuine 0% selling-cost sale (a private sale to family, say) in this tool: enter the smallest realistic cost figure instead, and note the difference. Everything else treats 0 honestly, including the rate: a 0% rate returns the loan divided by the number of payments.
Buy first or sell first
Sell first
- Proceeds are known to the dollar before you commit to the purchase
- No double mortgage payments, no bridge interest
- The cost: a possible gap between homes, temporary housing, and a rushed purchase once your sale closes
Buy first
- One move, no temporary housing, and time to prepare the old home for sale
- The cost: two mortgages at once, and usually a bridge loan or home-equity credit to reach the down payment
- Set the bridge toggle to Yes so the verdict records the plan honestly, then add bridge interest on top yourself
A bridge loan is short-term financing secured against your current home that covers the new down payment until the old home sells. It adds interest cost and a hard deadline, so it only makes sense when the numbers still work with that cost included. This tool flags the need in the verdict (“Feasible (Bridge Loan Needed)”) but does not price the bridge loan itself, which is a stated limit, not an oversight. On the purchase side, a seller credit or a rate buydown on the new loan changes the same closing table; the buy-down rate calculator prices that trade on the new mortgage.
What other buy-sell tools miss
Miss 1: the chain is split in two. Most tools do one side only: sale-proceeds calculators stop at net proceeds, and affordability calculators start from a down payment you type in, as if it fell from the sky. The number that decides a move is the join between them, proceeds versus cash needed, and that is the output this tool is built around.
Miss 2: no verdict, just arithmetic. A grid of figures still leaves you to work out whether the plan funds itself. The surplus line and the Feasible / Additional Cash Required verdict answer the actual question, and the shortfall case names the size of the gap.
Miss 3: the equity position change. Tools that celebrate a surplus rarely show that your equity stake can fall by $80,000 on a feasible move, as it does in the worked example. Seeing both numbers at once is what separates a plan from a sales pitch. Planning guides for selling and buying together, such as the Ready Steady Sell breakdown of the combined numbers, make the same point in prose: proceeds, deposit and borrowing have to be added up in one place.
Frequently Asked Questions
You need enough net proceeds to cover the new down payment plus closing and moving costs. The calculator compares net proceeds (sale price minus mortgage balance minus selling costs) against cash needed at closing; the difference is your surplus or shortfall. In the worked example, $198,500.00 in proceeds covers $167,000.00 in costs, leaving a $31,500.00 surplus.
Selling costs usually total 7 to 10 percent of the sale price: roughly 5 to 6 percent in agent commissions plus 1 to 3 percent in closing costs, transfer taxes, and fees. The calculator takes one combined percentage and defaults to 8 percent if the field is blank; adjust it to your market and your listing agreement.
Buying first avoids a rushed move but means carrying two mortgages, which is where a bridge loan comes in. Selling first is financially safer but can force temporary housing. Run the tool twice, once per order: set the bridge loan answer to Yes for the buy-first scenario and compare the feasibility verdicts.
A bridge loan is short-term financing secured against your current home that covers the new down payment until the old home sells. It adds interest cost and risk, so it only makes sense when the numbers still work with the extra cost. Toggle Need a Bridge Loan to Yes and the verdict notes that a bridge loan is part of the plan; the tool does not add bridge interest to the costs.
The tool uses the standard amortization formula: payment = loan amount times (r times (1 + r) raised to n) divided by ((1 + r) raised to n minus 1), with r as the monthly interest rate and n as the number of payments. It covers principal and interest only; taxes, insurance, and HOA dues are extra.
A negative surplus means your net sale proceeds do not cover the down payment plus closing and moving costs, and the absolute value is the extra cash you must bring or borrow. Options include a larger sale price, a cheaper target home, a smaller down payment, or a bridge loan, and you can test each one by changing a single input.
It compares the equity you hold now with the equity stake you will hold in the new home on day one (new price minus new loan). In the worked example it is -80,000.00. Of that gap, $31,500 went to selling costs and $17,000 to closing and moving costs, and $31,500 remains yours as surplus cash, which this line does not count. A negative figure is normal for a move up; a deeply negative one deserves a second look.
Add This Calculator to Your Website
References
- Veterans United, “Home Sale Proceeds Calculator” education guide – seller cost bands including commissions, and how proceeds fund the next purchase. Veterans United: Home Sale Proceeds Calculator Guide. Accessed October 2026.
- Ready Steady Sell, “Selling a House and Buying a New One: The Numbers (2026 Guide)” – the combined proceeds, deposit, borrowing and buying-costs method for a linked sale and purchase. Ready Steady Sell: Selling and Buying a House, The Numbers. Accessed October 2026.
- Beycome, “Sell Your Home Calculator: Maximize Profit, Minimize Cost” – the cost items that reduce seller proceeds and how equity estimates feed a next-home down payment. Beycome: Sell Your Home Calculator Guide. Accessed October 2026.
- Consumer Financial Protection Bureau, “Select the Kind of Loan That Fits Your Needs” – comparing loan structures for the new mortgage over the time you expect to keep it. CFPB: Select the Kind of Loan That Fits Your Needs. Accessed October 2026.
- LendingTree, “How Much House Can I Afford?” – front-end and back-end ratio checks to run on the new payment before committing to a target price. LendingTree: How Much House Can I Afford. Accessed October 2026.