Extend or Move Calculator
Compare the net cost of extending your home against the full cost of moving to a larger one, including every transaction cost.
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Needing more space forces a choice between building it and buying it, and the comparison is rarely made properly because the costs are shaped so differently. An extension costs a lump sum and returns part of it as value. Moving costs transaction fees on both sides plus the entire price step to a bigger property.
Extending usually wins on cost, sometimes by a wide margin. Moving wins when the extension would push the property past what the street supports, or when you want a different location anyway.
The comparison
Net cost of extending = build cost − value added. Net cost of moving = selling costs + buying costs + removals + the price step between the two properties. Both are expressed as what you are out of pocket for the extra space.
Worked example
A 60,000 extension adding 45,000 of value costs 15,000 net. Moving from a 400,000 home to a 500,000 one costs 20,000 in selling fees, 20,000 in buying costs, 3,000 in removals and the 100,000 price step — 143,000 in total. Extending is 128,000 cheaper for the same extra rooms.
The ceiling price is the limit
An extension only returns value up to what the street supports. If the largest homes nearby sell for 450,000, spending 60,000 to reach a notional 500,000 will not be recovered, and the value added should be set accordingly. Look at actual sold prices for the biggest houses in the area before assuming an uplift.
Put your number on the page that answers the question
Buyers remember whoever gave them the answer. A property page of your own carries this calculator, your listings and a WhatsApp button, so the next question comes to you.
Create your free property pageFrequently asked questions
Does an extension always add value?
No. It adds value up to the ceiling price for the street and very little beyond it. Poorly designed extensions that remove garden or light can even reduce value, so the uplift depends on the design as much as the size.
What does this comparison leave out?
The disruption of living through a build, the months it takes, the risk of overruns, and the fact that moving may deliver a different location or school catchment that has value of its own. It is a cost comparison, not a life comparison.
How accurate is the value added figure?
It is the least reliable input, so get it from a local agent who sells extended properties on your street rather than a national average. Testing the calculation at a lower uplift shows how sensitive the answer is.
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