How to keep an error log for GMAT and GRE quant
David Baum, founder of Roughwork · 25 October 2026 · 9 min readKeep one row per miss with five things in it: the question, the concept tested, the exact wrong step, a one sentence takeaway, and a date to redo the problem. Review the log twice a week, and redo every logged question cold.
Most people who miss a quant question do the same three things: wince, read the explanation, nod. Two weeks later they miss a different question to the exact same slip. An error log is the habit that breaks that cycle. It is one of the highest-return habits in GRE and GMAT prep, and almost nobody keeps one properly, because the useful version asks for a sentence of honesty per miss rather than a tally mark. This guide covers the format, the review routine, and two worked entries you can copy. It is part of our wider system for catching your own careless mistakes.
What is an error log?
An error log is a written record of every practice question you miss, one row per error, detailed enough that patterns show up when you read it back. It is not a score tracker or a list of hard questions. Think of it as a diagnosis file: for each miss, what exactly went wrong on the page, in words. The point is the read, not the write. After two weeks of honest rows you will find that most of your lost points come from two or three repeated slips, and that changes what you practice.
Why does an error log work?
Because it stops you from dismissing a miss, and the dismissal is the real problem. Mike McGarry of Magoosh names the trap: calling a miss careless is a way of deciding there is nothing to learn from it. His remedy is to write the mistake out in full:
“It would help to force yourself to articulate, in a journal, exactly what your mistake was and exactly what you need to remember to get a problem of this sort correct the next time: forcing yourself to write it down completely, in words, would build important connections across different parts of your brain.”
Mike McGarry, GMAT expert at Magoosh
Elaine Loh, who teaches the GMAT at Manhattan Prep, sees the same two benefits in her students:
“Error logging not only helps people become aware of careless errors, but it also helps them with concept recognition.”
Elaine Loh, GMAT instructor at Manhattan Prep
Awareness and recognition are two different gains. The awareness is about your slips: you learn which move your hand rushes. The recognition is about the test: naming the concept behind every miss trains you to name the concept behind every new question, faster. Both come from the same act of writing the row.
What goes in each entry?
Five columns, and Loh's names for them are hard to improve on:
“You'll need five columns: Question, Content Tested, What I Did Wrong, TAKEAWAY (yes, in capital letters), Re-do Date.”
Elaine Loh, GMAT instructor at Manhattan Prep
Taking them in order:
- Question. Enough to find it again: the source, the set, the number. You will need it on the redo date.
- Content tested. The concept, named. "Exponent rules," "distributing a negative," "rate with two machines." Naming it is the recognition training.
- What I did wrong. The exact step, not the category. "Dropped the flip when I opened the bracket" is a usable entry. "Careless" is not; it is the dismissal McGarry warns about, written down.
- TAKEAWAY. One full sentence you are going to act on, written as an instruction to your future self. This column does the work. A row without a takeaway is a tally mark.
- Re-do date. About two weeks out. Loh's framing is that the date is a scheduled meeting with the problem, and you redo it cold, with no notes open.
That is the whole format. One honest row takes about ninety seconds to write. The two entries below show what honest looks like.
Worked entry one: a sign error
The problem: solve 2x minus (x minus 7) equals 12.
The miss: you drop the bracket and keep the inside signs as they were, writing 2x minus x minus 7 equals 12. That gives x minus 7 equals 12, so x equals 19. Plug it back into the original: 2 times 19 is 38, the bracket is 19 minus 7, which is 12, and 38 minus 12 is 26. Not 12. The answer fails.
The correct line: a minus in front of a bracket flips every term inside, so minus (x minus 7) becomes minus x plus 7. Then 2x minus x plus 7 equals 12, which is x plus 7 equals 12, so x equals 5. Check it: 2 times 5 is 10, the bracket is 5 minus 7, which is negative 2, and 10 minus negative 2 is 10 plus 2, which is 12. It holds.
The log row:
- Question: practice set 4, question 11, linear equations.
- Content tested: distributing a negative across a bracket.
- What I did wrong: dropped the bracket without flipping, so plus 7 stayed as minus 7 and I solved a different equation.
- TAKEAWAY: when I remove a bracket with a minus in front, I write the flipped sign of every inside term before anything else.
- Re-do date: 8 November.
Notice what the row did. "Algebra mistake" became a specific move your hand makes under time pressure, and the takeaway is a drillable instruction. Sign errors are common enough to deserve their own guide, with three more worked examples: how to stop making sign errors on GMAT and GRE quant.
Worked entry two: an arithmetic slip
The problem: a machine fills 7 boxes a minute. How many boxes does it fill in 48 minutes?
The miss: you split the multiplication sensibly, 7 times 40 is 280, then recall 7 times 8 as 54 and write 280 plus 54 equals 334. The method is fine. One retrieved fact is wrong, and nothing in the method will ever flag it.
The catch is to redo the step a different way. Compute 48 times 7 as 50 minus 2, times 7: that is 350 minus 14, which is 336. The two routes disagree, 334 against 336, so one retrieval is wrong. Check the small fact: 7 times 8 is 56, not 54. Then 280 plus 56 is 336, and both routes agree.
The log row:
- Question: timed set 2, question 6, rates.
- Content tested: multi digit multiplication inside a rate problem.
- What I did wrong: recalled 7 times 8 as 54 and never checked it, so a correct setup produced a wrong answer.
- TAKEAWAY: on any multiplication that decides the answer, I redo it a second way before moving on; 7 times 8 is 56.
- Re-do date: 8 November.
After a few weeks the Content Tested column starts doing quiet work of its own. If the same concept keeps appearing, the misses were never careless. McGarry's point cuts the other way too: a repeated "slip" on one topic usually means there is something about that topic you have not fully understood. The log is how you find out which kind of miss you are looking at. The same format handles the other recurring types, misread questions, answering the wrong quantity, miscopied numbers, and we are writing those up guide by guide.
How often should you review the log?
Twice a week, per Loh, and the redo dates are appointments you keep. The review is two passes. First, read the TAKEAWAY column top to bottom and watch for repeats; a takeaway you have written three times is your next drill. Second, redo every question whose date has come up, cold, no notes. If you get it right, the row retires. If you miss it again, it gets a new row and a new date, and that is information too.
Budget more time for this than feels natural. Loh is blunt about the ratio:
“Your time spent reviewing and error logging problems should be about double what you spend actually doing the problems.”
Elaine Loh, GMAT instructor at Manhattan Prep
Double. Most people run the opposite ratio: hours of fresh sets, minutes of review. The sets feel like progress because they produce a score. The review is the progress, because it is the only part aimed at the specific points you keep losing.
Should you log questions you got right?
Log the ones you guessed on. Loh's advice covers every wrong answer and every lucky guess, and the guess matters more than it looks: a right answer you could not defend is a concept gap wearing a point, and on test day the costume comes off. The row is the same five columns, with "what I did wrong" replaced by what you did not know. Questions you answered with a method you trust can stay out of the log. The log should stay short enough to read, because a log nobody reads back is a diary, not a tool.
Paper or spreadsheet?
Whichever one you will still be updating in week four. A spreadsheet sorts by concept and counts repeats for you, which makes the weekly read faster. A notebook sits next to your scratch paper, which makes the entry likelier to get written at the moment of the miss, and the entry only exists if it gets written. The format is not the lever. The takeaway sentence and the kept redo date are the lever, and both fit on paper from 1980 as comfortably as in any app.
How Roughwork helps with your error log
The weakest link in any error log is the third column. "What I did wrong" depends on you finding the wrong step yourself, hours later, by rereading your own scratch work, and the step that slipped past your attention the first time slips past it again on review. Roughwork gives you practice with instant feedback on the quant you work out by hand. When a step is wrong, a dropped sign, a bad retrieval, a term that vanished between lines, it catches that step and explains what is wrong, and you make the correction yourself. It follows your written work line by line, so you learn which exact line failed while the page is still in front of you, which is precisely what the third and fourth columns of your log need. It does not do the thinking for you, it does not write the answer onto your page, and it does not keep the log either. The record stays yours to write and yours to read back, because the weekly read is where the value is, and it only works if it is yours. What Roughwork removes is the guesswork about what to write in the row.
Frequently asked questions
What is an error log for GMAT and GRE prep?
An error log is a written record of every practice question you miss, one row per error, with the question, the concept tested, the exact step that went wrong, a one sentence takeaway, and a date to redo the problem. Reviewed regularly, it turns a vague sense of carelessness into a short list of the specific slips that cost you points.
What should each error log entry include?
Five things: the question reference, the content tested, what you did wrong, a takeaway written as a full sentence, and a redo date about two weeks out. The takeaway is the column that does the work. A tally mark teaches you nothing; a sentence that names the exact wrong step does.
How often should I review my error log?
Twice a week, and redo every logged question cold when its redo date comes up. Review time should be generous: Manhattan Prep instructor Elaine Loh advises spending about double the time reviewing and logging problems that you spend doing them.
Should I log questions I answered correctly?
Log the ones you guessed on. A lucky guess is a miss wearing a right answer, and it hides a concept you have not secured. A right answer you earned stays out.
Do I need a special spreadsheet to keep an error log?
No. A notebook page with five columns works, and so does any spreadsheet. The format matters far less than the discipline of writing the takeaway as a full sentence and actually redoing the logged questions on schedule.
Does Roughwork keep the error log for me?
No. Roughwork follows your handwritten work line by line, catches the wrong step the moment it happens, and explains what is wrong, so the entry you write is accurate instead of a guess. The log itself stays yours to keep and review, because the weekly read is where the value is.
References and further reading
- Elaine Loh, "Error Log: The #1 Way to Raise Your GMAT Score," Manhattan Prep. The source for the five columns, the twice a week review, and the double time ratio quoted above. manhattanprep.com
- Mike McGarry, "Careless Mistakes on GMAT Math," Magoosh. His case for the journal entry. magoosh.com
- Roughwork, "How to stop losing GMAT and GRE points to careless mistakes (the hub guide this spoke supports)."
- Roughwork, "How to stop making sign errors on GMAT and GRE quant."