The most accurate method I've used is "1 week per page". This is for backend development and not web design. Surely such an overly simple estimate is going to

The most accurate method I've used is "1 week per page". This is for backend development and not web design. Surely such an overly simple estimate is going to be wrong? Well yes, but reality is complex and no calculation is going to capture it correctly. If you find 1 week per page is too inaccurate you can update your future estimates based on past performance.