Excel formulas acting slow? Today lets talk about optimizing & speeding up Excel formulas. Use these tips & ideas to super-charge your sluggish workbook. Use the best practices & formula guidelines described in this post to optimize your complex worksheet models & make them faster.
10 Tips to Optimize & Speed up Excel Formulas
1. Use tables to hold the data
Starting Excel 2007 you can keep all the related data in a table. For example call center data in our recent dashboard is kept in a table. Tables can be used in formulas with structural references, can be used as a source for pivot tables etc. And since tables grow & shrink as you add / remove data, none of your formulas need to be dynamic. As an example, if you have table called cs, then the formula sum(cs[column_name]) refers to sum of all values in the column_name of table cs. Even if you add more data to CS, the formula still works.
Resources to learn about Excel Tables:
- Introduction to Excel Tables – what are they and how to use them?
- Example: Customer Service Dashboard – Data & Calculations
2. Use named ranges, named formulas
By using names and named formulas, you can simplify your spreadsheet. Not only that, since named ranges & named formulas can hold arrays (ie lists of values), you can hold intermediate results or values that you need to refer many times in these named formulas. This will reduce the formula overhead and makes your workbooks faster.
Resources to learn about named ranges & named formulas:
- Excel School Program: In this comprehensive course, I talk about how to think about and write better formulas for data analysis work.
- Musings on Live Calendar [Excel Hero]
- Examples of Named Formulas – 2023 Calendar in Excel
3. Use Dynamic Arrays & Spill Ranges
Introduced in Excel 365, Dynamic Arrays allow us to build complex calculations with ease. I suggest incorporating new functions like:
- FILTER to fetch a list of values that meet one or more criteria.
- SORT to sort the values
- UNIQUE to eliminate duplicate values on the fly
- XLOOKUP to perform various lookups
- VSTACK / HSTACK to combine datasets
- TOCOL / TOROW to convert tables of data to single row or column formats
- # or Spill operator to manage spill ranges
Learn more about Dynamic Array functions here:
- Dynamic Array Functions – A deep introduction
- Dynamic Array Functions – how to use them [Video]
- How to use XLOOKUP
4. Use Pivot Tables
Many times, even when we do not need formulas we use them, because we can. Pivot tables are an excellent way to calculate a lot of summary values with few clicks. Once the pivot is built, you can refer to the pivot values with GETPIVOTDATA or simple cell references. This will reduce a lot of unnecessary calculations. If you are changing the data, you can just go to DATA ribbon and refresh all pivots in one go. This process works smoothly when you use tables to hold the data.
One of the reasons for slow workbooks is lot of data. Since, pivot tables are designed to work with lots of data, by using them, you can speed up your workbooks.
Resources to learn Pivot Tables:
5. Sort your data
One of the reasons for sluggish performance is that you are searching for something in a lot of un-sorted data. You are making Excel look for a needle in a hay-stack. Many times we inherit un-sorted data thru data imports. By sorting the data & using correct operators in lookup formulas, we can instantly speedup a sluggish workbook. If you feel that sorting the data is a pain, you can even automate it with Power Query or a sort procedure (thru a simple VBA macro).
Examples on Sorting:
- Remove duplicates & sort a list using Pivot Tables
- Use Power Query to pre-sort the data you are working with
6. Use Manual Calculation Mode
Speed is the hefty price you pay for complexity. But many times, we want our Excel workbooks to be complex, because only then they would reflect real world. In such cases, you can set formula calculations to manual mode.
Just press F9 whenever you want to run the formulas. Please note that Excel runs formulas whenever you save the file too.
7. Use Non-volatile formulas
There are a class of formulas in excel called as volatile formulas. These formulas are re-calculated whenever there is a change in the workbook. Examples of volatile formulas are RAND, NOW, TODAY, OFFSET etc. So when your worksheet has a lot of volatile formulas, any time you make a change all these formulas must be re-calculated. Thus, your worksheet becomes slow.
Solution? Simple, do not use volatile formulas. For example, instead of using OFFSET to construct a dynamic range, you can use INDEX. Since INDEX is non-volatile, it tends to be faster. Or better still, use a table.
Resources to learn more:
8. Keep formulas in a separate sheet
Formulas are the driving force behind any Excel workbook or model. By keeping all them in a separate worksheet(s), you minimize the chance of mistakes, omissions or repetitions. Debugging or investigating slow performance becomes an easy task when all formulas are in same place. I usually keep all the formulas in one sheet whenever I am designing a dashboard or complex workbook. This structure also helps me in thinking thru various calculations and planning the formulas in a structured way.
9. Write better formulas
Here are some guidelines that I follow when writing formulas.
- Built-in formulas tend to better than your own version – for example SUMIFS is easier to write and just as fast as SUMPRODUCT.
- Do not refer to entire column when you need just a few values. Do not write SUM(A:A), when you know values are only in A1:A10.
- IFERROR instead of lengthy IF(ISERROR formulas. Use IFERROR to simplify your error checking.
- Remove or Fix formula errors [how to, findout why formulas are not working]
- Use newer Dynamic Array formulas instead of old clunky array formulas
- Remove or Reduce references to other workbooks. Use Power Query instead.
- Remove any named ranges that result in error or missing links.
- Try to come up with alternative formulas: this not only sharpens your mind, but lets you discover better solutions.
- Do not calculate something if you do not need it.
- Do not calculate same thing twice. Use the first result second time too. Use LET for accomplishing this.
Resources to write better formulas:
- Introduction to SUMIFS formula
- Introduction to XLOOKUP formula
- How to use the new Dynamic Array functions in Excel
- Introduction to SUMPRODUCT formula
- Introduction to IFERROR formula
- Excel Formula Forensics
- Excel School program
10. Desperate times need desperate measures
Sometimes, no matter what you do, the workbook remains slow. Here are a few whacky ideas that I try in such cases:
- Replace formulas with values. I take a backup of the formulas. Then I select everything, CTRL+C, ALT+ESV (or CTRL Shift V). Done!
- Develop the workbook from scratch: Sometimes it helps to design the workbook afresh.
- Replace external data links with actual data: And import data by copy-pasting if needed.
- Reduce the functionality: See if the end user can live with fewer features in the workbook.
- Find an alternative solution: Trying to do everything in Excel is foolish. See if there is any external tool that can do this better & faster.
BONUS: Learn new formulas & play with them
Optimization is not a one-shot exercise. It is an ongoing-business. So you need to constantly learn new formulas, new uses & play with them. This way, you see new ways to improve a sluggish workbook. To begin with, explore our Formula homework & formula forensics pages and see how you solve these problems.
How do you speed-up your Excel formulas?
So how do you optimize & speed-up your Excel formulas? What techniques do you use? Please share using comments.
20 Responses to “Simulating Dice throws – the correct way to do it in excel”
You have an interesting point, but the bell curve theory is nonsense. Certainly it is not what you would want, even if it were true.
Alpha Bravo - Although not a distribution curve in the strict sense, is does reflect the actual results of throwing two physical dice.
And reflects the following . .
There is 1 way of throwing a total of 2
There are 2 ways of throwing a total of 3
There are 3 ways of throwing a total of 4
There are 4 ways of throwing a total of 5
There are 5 ways of throwing a total of 6
There are 6 ways of throwing a total of 7
There are 5 ways of throwing a total of 8
There are 4 ways of throwing a total of 9
There are 3 ways of throwing a total of 10
There are 2 ways of throwing a total of 11
There is 1 way of throwing a total of 12
@alpha bravo ... welcome... 🙂
either your comment or your dice is loaded 😉
I am afraid the distribution shown in the right graph is what you get when you throw a pair of dice in real world. As Karl already explained, it is not random behavior you see when you try to combine 2 random events (individual dice throws), but more of order due to how things work.
@Karl, thanks 🙂
When simulating a coin toss, the ROUND function you used is appropriate. However, your die simulation formula should use INT instead of ROUND:
=INT(RAND()*6)+1
Otherwise, the rounding causes half of each number's predictions to be applied to the next higher number. Also, you'd get a count for 7, which isn't possible in a die.
To illustrate, I set up 1200 trials of each formula in a worksheet and counted the results. The image here shows the table and a histogram of results:
http://peltiertech.com/WordPress/wp-content/img200808/RandonDieTrials.png
@Jon: thanks for pointing this out. You are absolutely right. INT() is what I should I have used instead of ROUND() as it reduces the possibility of having either 1 or 6 by almost half that of having other numbers.
this is such a good thing to learn, helps me a lot in my future simulations.
Btw, the actual graphs I have shown were plotted based on randbetween() and not from rand()*6, so they still hold good.
Updating the post to include your comments as it helps everyone to know this.
By the way, the distribution is not a Gaussian distribution, as Karl points out. However, when you add the simulations of many dice together (i.e., ten throws), the overall results will approximate a Gaussian distribution. If my feeble memory serves me, this is the Central Limit Theorem.
@Jon, that is right, you have to nearly throw infinite number of dice and add their face counts to get a perfect bell curve or Gaussian distribution, but as the central limit theorem suggests, our curve should roughly look like a bell curve... 🙂
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I'm afraid to say that this is a badly stated and ambiguous post, which is likely to cause errors and misunderstanding.
Aside from the initial use of round() instead of int(),.. (you've since corrected), you made several crucial mistakes by not accurately and unambiguously stating the details.
Firstly, you said:
"this little function generates a random fraction between 0 and 1"
Correctly stated this should be:
"this little function generates a random fraction F where 0 <= F < 1".
Secondly, I guess because you were a little fuzzy about the exact range of values returned by rand(), you have then been just as ambiguous in stating:
"I usually write int(rand()*12)+1 if I need a random number between 0 to 12".
(that implies 13 integers, not 12)
Your formula, does not return 13 integers between 0 to 12.
It returns 12 integers between 1 and 12 (inclusive).
-- As rand() returns a random fraction F where 0 <= F < 1, you can obviously can only get integers between 1 and 12 (inclusive) from your formula as stated above, but clearly not zero.
If you had said either:
"I usually write int(rand()*12) if I need a random number between 0 to 11 (inclusive)",
or:
"I usually write int(rand()*12)+1 if I need a random number between 1 to 12 (inclusive)"
then you would have been correct.
Unfortunately, you FAIL! -- repeat 5th grade please!
Your Fifth Grade Maths Teacher
Idk if I'm on the right forum for this or how soon one can reply, but I'm working on a test using Excel and I have a table set up to get all my answers from BUT I need to generate 10,000 answers from this one table. Every time, I try to do this I get 10,000 duplicate answers. I know there has to be some simple command I have left out or not used at all, any help would be extremely helpful! (And I already have the dice figured out lol)
Roll 4Dice with 20Sides (4D20) if the total < 20 add the sum of a rerolled 2D20. What is the average total over 10,000 turns? (Short and sweet)
Like I said when I try to simulate 10,000turns I just get "67" 10,000times -_- help please! 😀
@Justin
This is a good example to use for basic simulation
have a look at the file I have posted at:
https://rapidshare.com/files/1257689536/4_Dice.xlsx
It uses a variable size dice which you set
Has 4 Dice
Throws them 10,000 times
If Total per roll < 20 uses the sum of 2 extra dice Adds up the scores Averages the results You can read more about how it was constructed by reading this post: http://chandoo.org/wp/2010/05/06/data-tables-monte-carlo-simulations-in-excel-a-comprehensive-guide/
Oh derp, i fell for this trap too, thinking i was makeing a good dice roll simulation.. instead of just got an average of everything 😛
Noteably This dice trow simulate page is kinda important, as most roleplay dice games were hard.. i mean, a crit failure or crit hit (rolling double 1's or double 6's) in a a game for example dungeons and dragons, if you dont do the roll each induvidual dice, then theres a higher chance of scoreing a crit hit or a crit failure on attacking..
I've been working on this for awhile. So here's a few issues I've come across and solved.
#1. round() does work, but you add 0.5 as the constant, not 1.
trunc() and int() give you the same distributions as round() when you use the constant 1, so among the three functions they are all equally fair as long as you remember what you're doing when you use one rather than the other. I've proven it with a rough mathematical proof -- I say rough only because I'm not a proper mathematician.
In short, depending on the function (s is the number of sides, and R stands in for RAND() ):
round(f), where f = sR + 0.5
trunc(f), where f = sR + 1
int(f), where f = sR + 1
will all give you the same distribution, meaning that between the three functions they are fair and none favors something more than the others. However...
#2. None of the above gets you around the uneven distribution of possible outcomes of primes not found in the factorization of the base being used (base-10, since we're using decimal; and the prime factorization of 10 is 2 and 5).
With a 10-sided die, where your equation would be
=ROUND(6*RAND()+0.5)
Your distribution of possible values is even across all ten possibilities.
However, if you use the most basic die, a 6-sided die, the distributions favor some rolls over others. Let's assume your random number can only generate down to the thousandths (0.000 ? R ? 0.999). The distribution of possible outcomes of your function are:
1: 167
2: 167
3: 166
4: 167
5: 167
6: 166
So 4 and 6 are always under-represented in the distribution by 1 less than their compatriots. This is true no matter how many decimals you allow, though the distribution gets closer and closer to equal the further towards infinite decimal places you go.
This carries over to all die whose numbers of sides do not factor down to a prime factorization of some exponential values of 2 and 5.
So, then, how can we fix this one, tiny issue in a practical manner that doesn't make our heads hurt or put unnecessary strain on the computer?
Real quick addendum to the above:
Obviously when I put the equation after the example of the 10-sided die, I meant to put a 10*RAND() instead of a 6*RAND(). Oops!
Also, where I have 0.000 ? R ? 0.999, the ?'s are supposed to be less-than-or-equal-to signs but the comments didn't like that. Oh well.
How do you keep adding up the total? I would like to have a cell which keeps adding up the total sum of the two dices, even after a new number is generated in the cells when you refresh or generate new numbers.
So, how do you simulate rolling 12 dice? Do you write int(rand()*6) 12 times?
Is there a simpler way of simulating n dice in Excel?
I've run this code in VBA
Sub generate()
Application.ScreenUpdating = False
Application.Calculation = False
Dim app, i As Long
Set app = Application.WorksheetFunction
For i = 3 To 10002
Cells(i, 3).Value = i - 2
Cells(i, 4).Value = app.RandBetween(2, 12)
Cells(i, 5).Value = app.RandBetween(1, 6) + app.RandBetween(1, 6)
Next
Application.ScreenUpdating = True
Application.Calculation = True
End Sub
But I get the same distribution for both columns 4 and 5
Why ?
@Mohammed
I would expect to get the same distribution as you have effectively used the same function