Hello original poster ? What became of your polyp? I hope all was well  

For anyone else who may be reading this post, the guidelines for managing polyps are likely to change in the not too distant future. The original generally agreed guidelines were formed in 2017 using mostly low to moderate quality evidence and were likely a little too conservative, resulting in a whole swathe of people having their gallbladders taken out only to find out the polyps were benign in the majority of cases  - but by then you didn't care because you were relieved it wasn't cancer after the initially worry of being told you have a polyp that's growing. So if you do opt to have a cholecystectomy then don't worry too much as the Odds are overwhelmingly in your favour that the polyp will be benign, even if did seem to be growing. Obviously this isn't a guarantee but that is the nature of luck/kismet. Somebody sadly will be unlucky but for the majority of us, we will be fine.  
 

in recent years the evidence has started to accumulate that polyps can fluctuate in size and that growth of up to 4mm might even be part of the Natural progression of polyps. However when a sonographer tells you they've seen a polyp, it's very difficult to distinguish a true polyp from a "pseudo-polyp" which as essentially caused by cholesterol deposits building up in the wall of the gallbladder - they don't quite know what causes these and there doesn't appear to be any link to your blood cholesterol levels either from the limited evidence we do have. Anyway the true polyps, especially if they are of the type called adenomas, have the potential to turn malignant, much like bowel polyps can turn into bowel cancer. However, the actual risk of a polyp becoming malignant is actually pretty low overall. If you're very old, if you have primary sclerosing cholangitis, or are of Indian ethnicity (even this is very limited data from one Indian study many years ago which showed higher prevalence of of gallbladder cancer in people of Indian origin but the numbers looked at in the study were relatively small) - if you have any of these risk factors then you should speak with a surgeon if you have a gallbladder polyp which is showing signs of rapid growth - especially if it grows above 10mm in size (or 6mm if you have risk factors) - but don't have sleepless nights because in the majority of these gallbladders that are removed on the grounds of growth, very few turn out to be cancerous polyps. Some studies even show that none of the removed gallbladders showed cancer. 
 

As for size, well, longer term follow up studies done for monitoring people with chronic liver diseases pick up polyps from time to time and some of these will clear up on their own (meaning they were probably pseudopolyps all along), some will grow, some will shrink, some will be stable for years and then start growing. But the healthcare system can't keep scanning everybody forever so the guidelines advise when to stop following up. 
 

if you have no risk factors and it's less than 5mm in size then they will leave it be. From 6-9mm you will be scanned periodically either once or twice a year depending on your risk factors. Above 10mm seek an opinion. Most gallbladder cancer actually doesn't arise from a polyp at all and is equally common (albeit rare overall) in those with and without gallbladder polyps.  Traditionally growth of 2mm in a polyp has been considered the cutoff as anything less can be put down to differences in the operator or machine sensitivity etc. but more recent data does seem to show that even 2mm growth might well be within the normal range of natural variation for pseudo polyps in particular with some even arguing growth up to 4mm should be considered within normal limits based on the data we do have. . 

theres not enough evidence around wether having a single polyp or multiple polyps is riskier as far as potential for progression is concerned  

if you have a scientific background, look it up. JAMA articles from 2022 and also consensus radiology proposed guidelines from July 2022, though these may take a while to filter through to policy makers throughout different health care systems and countries. 
 

Gallbladder cancer is a pretty rare condition and whilst that's no consolation to those of us facing the difficult decision to go ahead with a cholecystectomy or not, many of us might well choose to have it out to take away the risk. And then live forever changed lives afterwards grateful that we didn't get gallbladder cancer. So ask your specialist about the risks of surgery and also in their experience, what proportion of removals have turned out to show cancer? Be informed fully and then make your choice. 
 

For those of you found to have a small polyp. Relax. 1 in 20 of us at least are walking around with these polyps. Yet only around 1 in 1000 men will get gallbladder cancer during their lifetime and 1 in 500 approximately women and sadly most gallbladder cancers in the UK at least are diagnosed in women (71%) (because they're more prone to inflammatory gallbladder problems and gallstones and chronic inflammation is often involved in the onset of many different cancers). But those unlucky souls who are diagnosed with gallbladder cancer will probably be older adults mainly  in their 70's and 80's (though it can occur at any age)  and will probably not have had a polyp that was the source of their cancer for most. 
 

so do get your polyp(s) followed up. But don't worry too much.