Do you live with insulin-dependent diabetes, count your carbs accurately, but still struggle with postprandial (after meal) high or low blood sugars?
If so, your “insulin-to-carb ratio” may need adjustment.
Your insulin-to-carb ratio is a number that tells you how much rapid-acting insulin you need to cover a specific amount of carbohydrates. It’s what allows you to accurately dose insulin for meals or to correct high blood sugars.
In this post, I will cover what your insulin-to-carb ratio is, how to find yours, factors that can influence it, and the available tools and mobile apps that can help you find and keep track of your ratios.
If your doctor is the one changing your insulin-to-carb ratios, a lot of the information we’ll discuss in this post will be relevant to bring to your doctor so that he or she can make informed changes to your diabetes management.
What is an insulin-to-carb ratio and why does it matter?
Your insulin-to-carb ratio (also just called a “carb ratio” or “carb factor”) indicates how many grams of carbs one unit of rapid-acting insulin covers to ensure that your blood sugars stay in your desired range.
Your carb ratio is often initially set by your doctor when you are diagnosed but should be updated regularly (if needed). A carb ratio of 1:10 means that 1 unit of rapid-acting insulin will cover 10 grams of carbs. A higher ratio indicates that you need less insulin to cover your carbs.
Let me give you an example:
If my carb ratio is 1:10 and I’m eating 30 grams of carbs, I’ll need 3 units of rapid-acting insulin to cover the meal (30 divided by 10). However, if my carb ratio is 1:15 I’ll only need 2 units of rapid-acting insulin (30 divided by 15)
That a higher carb ratio means less insulin can take a little time to wrap your head around but it’s an important fact when you start adjusting your carb ratio(s).
If you time the peak of your insulin with your meal, an accurate carb count combined with an accurate carb ratio will mean that your blood sugar should stay within your desired range and below 180 mg/dl (10 mmol/L).
If the timing of your insulin for the meal is off, but your carb count and carb ratio is right, you might see your blood sugar go slightly out of range but it should be back in range within 90 minutes (which is the average time insulin peaks.)
It’s also important to note that you should subtract the fiber content in your meal from your total carb count before calculating your insulin dose because fiber doesn’t break down completely in your digestive system and therefore does not raise blood sugar levels. Dosing for fiber could lead to low blood sugar.
How to calculate your carb ratio(s)
If you suspect that your carb ratio is off (often running high or low after meals could be a good indicator of that), it’s time to collect data in the form of blood sugar readings and do some analysis.
If you want good results you need good data, and you’re the only one who can collect it. As with most other things related to diabetes, it requires work but it’s worth it.
I suggest following the 4 steps below for 3-5 days minimum to collect data for you or your doctor to assess whether your carb ratio is correct. If you and/or your doctor don’t see any trends after 3-5 days, you’ll have to collect more blood sugar data.
- Focus on one meal at a time (breakfast for example). Try to enjoy the meal at roughly the same time each day and eat the same foods and quantities for the data collection period (this is why breakfast is a good place to start as it is easier to eat the same thing for breakfast each day)
- Make sure your carb count is correct and stick with the same carb ratio for the data collection period
- Try not to do anything that impacts your blood sugar significantly right before or after the meal (like going for a run)
- Be on top of your blood sugar measurements or Continuous Glucose Monitor (CGM)
- Measure your blood sugar before the meal
- Measure your blood sugar after the meal (90-120 minutes after your injection)
After 3-5 days, you should have enough data to start assessing whether your carb ratio for this time of day is accurate.
When you or your doctor does the analysis, you’ll focus on whether your blood sugar was in your desired range before the meal and whether your blood sugar came back into your desired range within 90-120 minutes of your insulin injection.
Note: I try not to take correction insulin doses when testing my carb ratios since it makes it harder to assess whether the carb ratio is accurate, but if your blood sugars are dangerously high or just higher than you’d like them to be, then go ahead and correct. You can always continue your carb ratio experiment another day. Always safety first!!
Let’s look at 2 different scenarios, assuming a meal of 30 carbs (that’s counted as accurately as possible) and a starting carb ratio of 1:10.
Blood sugar in-range before the meal, but high 90-120 minutes after
If your blood sugar is not back in range or coming down quickly 90-120 minutes after your meal, your carb ratio is too high. You can consider trying to experiment with ratios below 1:10, maybe 1:9 or 1:8 is the right ratio for you.
I don’t like to change my ratios too drastically since I’d rather run a little high for a few days than end up with a nasty low blood sugar. Remember, the lower the carb ratio, the more insulin you need per gram of carbs.
Blood sugar in-range before the meal, but low 90-120 minutes after
If your blood sugar is lower than your target range 90-120 minutes after your meal, your carb ratio is too low. You can consider trying to experiment with ratios higher than 1:10, maybe you need to go to 1:11 or 1:12. As mentioned, I usually do small incremental changes.
You also need to consider if your timing for when you take your insulin is off. If you have low blood sugar within 30-60 minutes of your injection, your food might not have been sufficiently digested yet and will hit your bloodstream later. You can assess this by measuring your blood sugar frequently and experimenting with taking your insulin a little later.
Note: The carb ratios listed here are just examples. You can have ratios much higher or lower than 1:10.
Things that influence your carb ratios
Our bodies change over time and so do our eating and exercise patterns. As your body and daily routine change, you might find that your carb ratio(s) needs to be adjusted.
Here are 5 things that can influence your carb ratios:
Time of day
You might have noticed that I write “carb ratio(s)” because most people have more than one carb ratio. For example, many are more insulin resistant in the morning so they might need a lower carb ratio for breakfast than they do for lunch or dinner.
In theory, you can have as many carb ratios as you like, but most diabetes devices (pumps, apps, smartpens) have a limited number. Mine has 4 and I utilize the 3. I have my lowest ratio for breakfast and the highest ratio for dinner and overnight.
Time of month (for women)
The fluctuating hormone levels of your menstruation cycle can have a significant impact on your blood sugars and your insulin needs. This can mean that you need different carb ratios (and most likely basal insulin) for periods where you’re extra insulin resistant due to hormonal changes.
I’m one of those women who see large differences in my insulin needs throughout my cycle. I need significantly less insulin the day(s) right before my period and always need to increase my carb ratios.
Type of meal: the impact of protein & fat
Carbs might be what’s converted into glucose in the bloodstream the fastest, but it’s not the only macronutrient that can impact your blood sugar.
If you eat large amounts of protein, you’ll most likely need to inject insulin to not see an increase in your blood sugar.
If you add large amounts of fat to your meal, you’ll most likely see a delayed release of the glucose into your bloodstream, which for many people means that they need to take two insulin doses rather than just one (one with the meal and one some time later).
Exercise/movement
If you’re more or less active than normal, you should consider that when you calculate your insulin doses. If you take your bolus insulin 30-60 minutes before a workout, you often need to reduce your dose by 25-75 percent. That’s a huge range and you’ll need to find the right reduction for you.
It’s worth mentioning that if you do resistance training or interval training, you might not need a reduction, you might even need an increase as these types of workouts can make blood sugars increase.
Bodyweight
If your body weight changes significantly, you’ll most likely see that your insulin needs change as well.
If your body fat percentage increases significantly, you might experience that you need more insulin to cover your meals. If you gain a significant amount of muscle mass, on the other hand, you might see that you need less insulin to cover your meals.
Tools to help you find and remember your carb ratios
Using carb ratios is pretty straightforward if you use an insulin pump to manage your diabetes. Most pumps have a built-in bolus calculator (calculates your suggested dose) and your medical team should have set it up for you and trained you on how to use it. If that’s the case, you just need to focus on whether your ratios are accurate.
If you manage your diabetes with manual injections, you need to look elsewhere for a “carb calculator” or memorize or write down your ratio(s). The benefit of a good calculator is that it can keep track of active insulin (insulin lasts 3-5 hours in the body) and can help keep track of your injections and ratio(s).
Mobile apps: There are no FDA-approved standalone apps that are approved for dosing recommendations in the United States, but I have used RapidCalc (not FDA-approved) and found it to be accurate and easy to use.
Outside of the United States, good options are the Hedia and MySugr apps.
Smart insulin pens: Companion Medical’s InPen is a smartpen available in the US only. It has all the functionalities of a pump, except for actually pumping, so it automatically keeps track of active insulin and has a bolus calculator. It sends the data directly to your phone via Bluetooth.
Smart meters: Some blood glucose meters also have bolus calculator functionalities or have an app that links with the meter.
Don’t expect perfection!
I know this post may have given you a lot to think about – and possibly work on. I recommend starting small and including your medical team as much as you need to.
A good place to start could be your breakfast carb ratio. Once you think you have that down, you can move on to lunch, then dinner, and then snacks.
And you won’t always get it right. We don’t have full information on what’s going on in our bodies and some days, your usual ratios won’t work. That doesn’t mean that they’re not right for you, give it a few days to see if things return to normal.
But if you keep experiencing high or low blood sugars after meals, it might be time to tweak your insulin-to-carb ratios.
Julie hayward
I am just starting the process of a insulin pump and I’m so confused on how to do the ratio carbs and counting all the things that I have to figure out I am legally blind so I do have issues with trying to look at lists and then calculating everything together so if you have any suggestions or any other advice please let me know thank you.
Christel Oerum
The pump manufacturer or your doctor’s office should be in charge of setting you up with your initial settings and teaching you how to use the pump. It’s not recommended that you start using an insulin pump on your own. It’s a fairly complex device and talking it over with a medical professional is needed for it to be safe
Rhonda Hammonds
Good Morning, I just found you this morning and am very thankful to do so! My son is 45 yrs old and a T1D since age 9. He is blind in his left eye and we are battling to save his right eye. His wife passed on March 1st and I moved him in with me. (I am on disability because of a prior cancer battle.). He was not under a a doctor’s care since he moved out of my home over 25 years ago. I am soaking up your information!
I do need help since He is now seeing a local endocrinologist and she recommends a 1:20 carb ratio 3 times a day with his bolus dose to be 6 units 30 minutes prior to the 3 meals.
I do find it hard to see how to prepare 120 carb meal 3 times a day for him.
Does this sound reasonable or did we completely miss what she wrote and told us? He is a very thin person.
Thank you.
RHonda Hammonds
Christel Oerum
Hmm, I wonder if the doctor wrote it up wrong. You’re right, 6 units at a 1:20 carb ratio would be 120 grams of carbs which might be more than he can eat in each meal. I’d suggest you contact the doctor and confirm, you could ask: “I just want to confirm that we have the right understanding of your guidance. We’d like for my son to eat according to his appetite and plan on diligently counting his carbs. That means we could apply the 1:20 carb ratio to each meal and snacks, meaning that if he only eats 60 grams of carbs for a meal, we’d dose 3 units 30-min before the meal. Is that in line with your guidance?”
I would personally hate to be forced to eat the same amount of carbs for each meal or be limited to only 3 meals daily. The benefit of carb counting is that you can eat who ever many times you’d like and how much you like. I hope you get clarification from the endo
Lone
Hi thanks for all your good advice! My 7 year old daughter just started on a pump medtronic 780 , she has it now 2 months and it seems she is needing much less insuline than before on the pen … how come..?. before her ratios were morning; 1:9, midday: 1:12, evening :1:20 , she is not doing other activities than before … she is now on morning: 1:12, midday 1:18, evening : 1:28 It seems it keeps going up ..we also prolonged the active insuline time with increments of 15 minutes seems to work better so that she does not hit lows That often.
Christel Oerum
Congrats, I’m so happy to hear that she’s thriving using an insulin pump. I’d guess that it comes down to her basal insulin. When on a pump both basal and bolus are from rapid-acting insulin. She might be better titrated when it comes to her basal or only using rapid-acting insulin might work better for her body. Regardless, good thing that you’re adjusting her ratios to her new normal
Avril
Just found your site – thank you for the information
I am still not sure how to calculate the carb/insulin ratio. For instance, I only eat one carb a day – one slice of whole-wheat bread for breakfast; plus try to eat only two fruits – peach or pear per day.
I have type 2 diabetes for about twenty years; and brought my AIC from 9 down to a steady 6.1 or 3 for two years.
I inject about 8 units of long lasting insulin every night before bed.
I have tried to download an Insulin Calculator into my phone; but asks what my carb/insulin ratio or what is my sensitivity factor? Have no idea; can you please help me.
Thanks.
Christel Oerum
If you don’t use rapid-acting insulin for your meals insulin-to-carb ratios won’t do anything for your diabetes management as such. If you do, the focus is to determine how many units of rapid-acting insulin (like Humalog, Novolog, Apidra, etc.) that you need per gram of carbs. So a slice of toast might have 15 grams of carbs (depends on the brand, look at the nutrition label), and if you find that you need 3 units of rapid-acting insulin to cover that your insulin-to-carb ratio is 5 (15 grams divided by 3 units)
Sandy
Thank you for the great information. ( Diagnosed with type 1 5months ago). Am following along with the current challenge as best as I can given my work schedule and the time difference of online webinars. I tend to catch them more on Youtube. I am still at the point where I am waiting for cgm approval. So I often just do manual finger pricks to look at my bg after meals. Still trying to get my head around how my various ratios (different for all 3 meals) and how my various activity or not affects my bg. I do find during the week having to be confined to my desk, makes a difference to how my body responds to post meal spikes. In any case thank you for your great information on your site.
Christel Oerum
You’re welcome Sany. Sounds like you’re using insulin pens. If you’re in the US I’d recommend looking into getting an InPen (a smart insulin pen) to help you keep track of all of your doses. If you’re outside the US the RapidCalc app might be a good resource, I used it for years. More on that here: https://youtu.be/68QUSn3PdjM
Linda
What perfect timing! I was planning to ask Gary about testing carb ratios this afternoon, but you answered my question. Thank you.
Dylan
Hi Christel,
I’m a Type-1 diabetic and have been for almost my entire life (diagnosed at 2 years old and I’m 30 this month!). I have been doing intermittent fasting and strength training for a number of years, but recently I’ve noticed some weird patterns. Today, for instance, I woke up with high blood sugar (250) and had to give myself a dose of fast-acting insulin before my workout in the morning (90 minutes). I checked myself after the workout and before lunch (when I break my fast) and my reading was 144, so I gave myself the insulin for it and went for around a 4 km walk. By supper, my blood sugar was spot on (90), but this is the weird part – it shot up to 288 around three hours later! This has been a recurring pattern that I really don’t understand. I’m relatively inactive for the three-four hours after supper, but I don’t see why that small window of inactivity would create such a dramatic jump in blood sugar when I’ve been more or less active all day. Any help or advice would be greatly appreciated.
Christel Oerum
if this is a new, and consistent pattern, you might want to have a look at your basal insulin. As we age, our routines change, body composition change, etc. our basal needs will change as well.
Jane
Could you elaborate on this. Still have unexpected highs at odd times.
Christel Oerum
To manage blood sugars you need to adjust both your long-acting (your basal) as well as your rapid-acting insulin to your daily needs.
Your long-acting insulin should keep you steady outside meals, so for example, if you drop or rise overnight it’s probably your long-acting insulin that needs adjusting.
Patricia
Christel, Thank you for Diabetic Strong!!! So much GOOD information every time. My ratio has been sliding down in the last few years and it really concerns me. Exercise is my biggest push right now. Thank you again for all you do for us.
Isa
Hi Christel, are you using a smart pen? I requested information. Do you think is a good option. Please advise. Thank you much and keep safe and healthy.
Christel Oerum
I’ve been using the InPen for about a year and highly recommend it for anyone using pens to manage their diabetes. It can really help with dose calculation, analytics, and daily management. I showed the reports on the Diabetes Strong Facebook page April 23rd if you want to see what those look like
Michelle Munro
Just a quick THANK YOU Christel… I reached out to you in a sleep-deprived, new T1D mom mess just over a year ago when my 3 year old son had just been diagnosed… You told me that “It’s a tough diagnosis but it gets easier”. I swear I have learned more from your emails and articles since then, than from the dozen Diabetes books I’ve read… Thanks again for your invaluable firsthand knowledge, practical advice and easy to digest info. Speaking of “digesting”, can’t wait to try out some of these recipes with my little guy as part of our new homeschooling curriculum! Lol First up, Fat Bombs!! 🙂
Christel Oerum
Wow Michelle, thank you so much for taking the time to write and check-in. I’m glad Diabetes Strong has been a resource for you and that you made it successfully through the first year. Sending hugs and enjoy the fat bombs 🙂