By calculated I mean he made a decision to do what he did while in his normal frame of mind. I don't believe there was any delusion, distortion due to drugs, or separation from reality. And I base that on several factors.
1. He remembers what happened. We can tell that because he has an excuse for the evidence - he knows what time it happened so he has a story to account for how long he was awake and busy before the attack started, he knows where the knife ended up so he has a story of pulling it out of his side and dropping it, he knows what order the family were attacked in because he has the scenario to fit and merely replaces himself with the attacker.
2. He made a plan. If he hadn't removed Sasha the dog before he attacked the family she would have been covered in blood, left paw prints everywhere in blood, and would probably have barked and raised the neighbours. He coped single handed with four people, three of whom were up and able to run. Just one escapee would have seen him jailed for life, so he had a plan for it.
3. He did quite a good clean up job. Left enough so that it wouldn't look cleaned up, but left no prints on the axe handle and only one on the knife blade. There were hardly any blood traces left in the shower. I haven't heard that he left bloody foot prints in his bathroom, or if he did I've forgotten.
4. He was methodical. He knew to harm himself (but was inhibited and avoided tender places) and harmed himself after showering so that family blood would be washed away but there would be blood on him from his own wounds so he wouldn't look showered.
5. He made immediate google searches before his 3 hour wait, which I wouldn't expect from someone in a psychotic state.
6. It followed a family argument, so there was probable cause.