you would have to ask a GM
How to calculate like a GrandMaster? ("I want to improve my calculating.")

You cannot calculate like a Grandmaster with 1 month of practice, it takes a lot of time. And, it is too challenging for 1800 Chess.com. If you want to know what it takes to calculate like a GM, do the book by Jacob Aagard, you'll understand what I mean.

I want to know too. I always get the general idea of a puzzle, but make a small mistake in the execution. I'd like to erase those small mistakes, they are holding back my puzzles rating.

Improving calculation skills is a key part of becoming a stronger player. Grandmasters are exceptional at calculation because they practice systematically and develop habits that help them think deeply and accurately. Here are some tips to help you improve:
1. Understand the Position First: Before calculating moves, assess the position. Identify key factors like king safety, weak squares or pawns, potential tactical motifs (pins, forks, discovered attacks).
2. Visualize Ahead: Work on visualizing positions a few moves ahead. Start small—calculate 2-3 moves deep, then gradually increase complexity. Blindfold chess or solving puzzles without moving pieces on the board helps improve visualization.
3. Candidate Movesl: Always consider multiple options instead of focusing on the first move that looks good. Ask yourself, "What are all the possible moves I can play here?" and evaluate each one.
4. Follow a Calculation Tree: Structure your calculations like a tree. Start with one move (the trunk). Explore responses from your opponent (branches). Continue until the position simplifies or you see the result. Write down variations during practice to spot errors and gaps in your thought process.
5. Eliminate Unrealistic Moves: Grandmasters don't calculate every move—they discard lines that are clearly inferior. Train yourself to quickly recognize moves that don’t contribute to your position or fail tactically.
6. Solve Tactical Puzzles Regularly: Tactical puzzles improve your ability to calculate efficiently. Focus on solving a mix of easy and complex puzzles, aiming to see the solution without moving pieces. Websites like Lichess or Chess.com offer excellent puzzles and exercises.
7. Practice Calculation Drills: Use books like Think Like a Grandmaster by Kotov or Perfect Your Chess by Volokitin to practice solving complex positions. These exercises mimic in-game calculation challenges.
8. Play Longer Time Controls: In blitz or bullet games, you focus on intuition rather than calculation. Playing classical games or daily chess gives you the time to practice deep calculation.
9. Analyze Your Games: Review your games and identify where miscalculations occurred. Try to re-calculate the critical moments without engine help, then compare your analysis to the engine's suggestions.
10. Stay Focused Under Pressure: Train your concentration with tactics or positions under time pressure. Learning to calculate efficiently when stressed mirrors tournament conditions.
Calculation is a skill that improves with consistent practice. The key is to be patient and deliberate in your training. Good luck!

okayy, instead of calculating like a grandmaster, how can i calculate like an IM or NM???
Not possible at your level.

In general, it is not possible to calculate at a level more than 500-600 points above your actual rating.
If you're a 1200, the best you will calculate is like a 1800.
The level difference is huge, and you need to do it step-by-step.
Also, if you really want to improve your calculation to new heights, you must work on it for at least 1.5 hours a day. And I don't mean doing random tactics, no, you should spend a good 15-20 on one position to calculate and consider the position carefully. (This does not mean you sit on a simple position for this long, you must work on positions that are difficult, and in my opinion, these do not qualify under the category of 'tactics'.)

okayy, instead of calculating like a grandmaster, how can i calculate like an IM or NM???
It will take months to years to improve your calculation.
I've learnt this the hard way, I did not seriously work on calculation for a period in my career and I couldn't even properly calculate 3 moves ahead. Also, I would like to paraphrase something written in the book 'Forcing Chess Moves'
'If you are able to calculate the next 2 moves with absolute precision without making even one objective error, you are already performing at the tactical level of a Candidate Master'
That's why, after you're done with your calculation training or tactics, some people like to do studies or Find Mate in 2 studies (the hard ones, not the easy ones)
How do I calculate like a GrandMaster???