I've done 3 Ikea kitchens. do your design using their online tool, you can then log in at the store and have an associate look at the design and help you with details including fillers.

You don't need fillers between cabinets at all regardless of doors/drawer combos.

you only need fillers if the cabinets don't meet the wall, or if you use certain types of corner cabinet options. You do generally need space between an opening door of a fridge and a wall, and a cabinet and a wall to ensure clearance, but this can be achieved by the thicker end panels for a nice finished look.

The fronts are full overlay and the filler they supply sits flush to the cabinet box. I have typically purchased extra thick end panel to bring the filler strip to the level of the door/drawer fronts making it look more "finished."

there are different ways to do the fillers: thin end panels sold as wall or base end panels, thick end panels sold as panels for fridge or tall cabinet, and using pieces of door fronts cut to the filler size. I have spent extra and have cut down thick panels and fronts to use as filler - this looks less Ikea and more custom. (I hope this makes sense...)

if you live far from IKEA, take a day off during the week, like a Tuesday or Wednesday, drive out, and get there when they open.

bring along photos of your kitchen with existing doors/trims/windows and make sure you measure more than twice.

a sales associate will review your plan and tell you where you need trim pieces

There are also a number of online design companies who will do the design and planning for you for a fee. Probably not necessary if you are a good precise planner, and are prepared to crowd source your design ahead of time, but depends on what your personal time is worth.

I would spend lots and lots of time on the front end.

This was extremely helpful. Thank you for taking the time!

And - buy a few extras of the trim pieces. They are inexpensive and nothing worse than needing them and not having them...

Check out the IKDO website, too - they have lots of useful hints and ideas buried in their blog, and they will take your design and improve it immensely, from what I've observed over the years.

If your filler "needs" to be more than a couple of inches, consider shaving a couple of inches off another cabinet and putting their 9" wine rack in against a wall instead. You don't have to put all its shelves in, and it's very handy for chopping boards, trays, cookie sheets, etc. Link below.

Push for a knowledgeable designer when you go to Ikea, because a lot of them aren't, unfortunately - I suspect the good ones get snapped up by local independents who pay better and let them be humans. :/

9" base cabinet

"Everything you wished you knew about trimming out Ikea, but didn't know to even ask"

regarding IKD, that's a great idea, bubblyjock.

here is a photo from their website that demonstrates some filler/trim issues:

https://inspiredkitchendesign.com/spacious-ikea-kitchen/

https://inspiredkitchendesign.com/wp-content/uploads/2018/01/After-3-1000x750.jpeg

starting at the left side of the photo:

1. first cabinet to left of microwave

There is a trim piece under the cabinet, also called "light rail' there appears to be a metallic customization on the light rail (I think...) I'll bet you can do this with automotive tape (??) would love to hear someone else weigh in on this.

2. microwave

there is a thin end panel on both sides of the microwave, these are wall end panels.

there is also a strip of filler between the microwave and the cabinet bottom, this can be done with thin end panels, light rail, thick end panel, or toe kick filler, depending on how you want it to look. You can recess this filler to the level of the cabinet box or bring it flush with the door fronts, in this case it appears to be recessed. *** this item is a customization, if you use the IKEA planner, there will be no way to place this trim piece, you will have to account for it and plan for it separately. You can use a strip of an end panel, leaving more finished edges for other creative uses.

3. over the sink

each side of the over-sink cabinet has a side panel, and there is light rail trim under the over-sink cabinet.

4. ceiling

there is filler above all of the cabinets at the ceiling line. This is generally done with toe kick, however, it is recessed to the level of the cabinet box. If you want a different look, you can overlay slivers of cabinet doors, or slivers of tall panels over this trim to bring it flush with the cabinet door - different look.

5. inside corner

there is filler - either toekick or panels, at 90 degree angle on upper and lower inside corner. Again, here you may create a different look by overlaying slivers of cabinet door fronts or side panels. *** if you wish to do this pay attention to the thickness of the two types of side panels and the door fronts and make sure you are applying matching pieces, especially for a high end modern/uniform look. I did find it worth the money to buy additional door fronts for this type of filler (door fronts are > $$'s than panels/toe kick). *** if you are using wood grain, pay attention to direction of the grain on the panels/door fronts if you are concerned (read "obsessed") about uniform look (ask me how I know this...)

6. Fridge

Notice the flanking tall panels, the over-fridge cabinet is a bridge between these panels. you may not notice that there is also a panel under the over-fridge box hiding the cam hardware that is used to put the cabinet together. *** this under cabinet panel is not included in Ikea planning software, you will need to account for it separately. Just as with the microwave, you can recess the front edge of this panel or bring it flush with the cabinet doors for a different look. *** be really careful when you order your fridge, make sure to look at how tall the TOP edge of the hinge is so that it clears the underside of the over-fridge cabinet, you may or may not have space for additional trim panel. the fridge in the photo looks short-ish. I also don't really like that huge gap between the fridge and the cabinet bottom. this can be trimmed out.

7. toe kick

nothing to say, but you do need it.

8. buy at least 1 extra tall end panel if you have space to store it. This will accommodate possible future changes. It may also potentially save you from nuclear disaster. well, maybe not.

9. now that you have a new-found appreciatio

n of filler/trim/panels, spend some time looking at Sneidero, Bulthaup, and other higher end European brand web sites and think about how they use their trim pieces to achieve certain looks. You can do the same with Ikea for a fraction of the cost.