A survey of local authorities concluded that overall capital costs could be as high as £114m - significantly more than the £61m suggested by ministers.
The discrepancy comes almost five months after the Scottish Government announced a commitment of 600 hours of early learning and childcare for up to 27 per cent of two-year-olds.
While welcoming the policy's good intentions, council umbrella body Cosla believes the Scottish Government have made incorrect assumptions regarding the cost of additional buildings and splitting provision between local authority and private providers.
Speaking before a meeting of Holyrood's finance committee today, Scottish Conservative finance spokesman Gavin Brown said: "The Scottish Government rushed through this childcare commitment without any thought for how much it would cost to upgrade buildings and create the new facilities needed. It has now taken them five months to finally come up with a capital figure, yet there are concerns from Cosla that this cost could be even higher."
A Scottish Government spokesman said: "We are committed to investing £280m over two years to expand funded early learning and childcare for three and four-year-olds - from 12.5 hours to almost 16 hours a week - from August, and to extend this entitlement to the 27 per cent most vulnerable two-year-olds, reaching about 15 per cent in the first year."