Shares in the FTSE 250 company sank 22¼p to 108¼p, their lowest since it listed in November 2015 at 180p.
It has begun the search for a successor to Clive Fenton, 60, who took over four years ago having spent nearly three decades with Barratt Developments. He will step down at the end of August.
McCarthy has come under pressure as weaker pricing and economic uncertainty have prompted buyers to wait.
It said: “Customers have exercised more caution due to ongoing economic uncertainty, a slower secondary market and a softening of pricing, particularly in the South-east.”
A proposed ban on ground rents has also dented confidence.
McCarthy sells most properties leasehold.
The freehold is sold to private companies.
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Fenton said: “We have made great strides in growing the business and increasing supply into the market. Unfortunately... with the additional challenges posed to the business by the proposed ban on ground rents, it is clear that the group must embark on a new strategy to carry it safely through the next five years and beyond.
“Having reached the age of 60, it is right that I now stand aside to enable a new chief executive to be responsible for this journey. I have no absolutely no doubt that the group will have a successful future.”
McCarthy, which began a strategy review in April led by chairman Paul Lester, expects to make an annual operating profit of £65-80million, down from £96million last time.
It is aiming for sales of 2,100 to 2,300 compared with 2,302 legal completions the previous year.
Russ Mould, investment director at AJ Bell, said: “You may have thought building properties for people in retirement would be a simple, steady growth business. This would suggest this activity is not bulletproof.”