We assoom
- forces of both sides more or less of the same tech level. Ru has advantage in aviation, artillery, loitering ammunition drones and ability of long range strikes of limited effectivity. Ua unique advantage is intl of the whole NATO, including satellite, and very precise HIMARS which they can use to disrupt logistics but there's to few of them to affect direct combat. So Ru advantage affects direct combat more than Ukrainian.
- 25% of available forced dont participate in direct combat on the East and South (they don't man trenches and tanks and don't do assaults). these 25% include everything from support units to artillery, reserves and units taken to the rear for replenishment. Also tehy include units in raining, in Belorussia and on teh border of Belorussia. Some of these units such as artillery take some losses and affect what happens in close combat battlefield, but the losses are much less than infantry and tank units take.
- To have a good chance in assault one should have advantage of 3:1 unless it has signifficant superiority in hardware or advantageous terrain. Let's assoom that for Ukraine it should be closer to 3:1 as they don't have aviation and they have less arty, but they can hit logistics. For Russia it is 2:1 or even 1.5:1 as besides advantages in arillery and aviation Russia has 4x more potential manpower reserve.
- As soon as one side has nessessary advantage it assaults other side as it is not wise to just sit and wait for arrival of freshly trained reserves


Late SUmmer-Autumn, just before Kharkov and Kherson

Ru base numbers 200k - Reported by the US intl 185k + auxiliaries

Ua base numbers 600k - Reported by Ua themselves

25% support for Russia = 150k first line men
25% support for Ukraine = 450k first line men


Ukraine could make swift advances in Kharkov but it didn't fare that well in more fortified areas such as Kherson. They tried to advance in Kherson in the same time so they assoomd they had enough numerical superiority both there and in Krarkov.

Let's assoom they used to have at least 3:1 superiority (likely more) as they advanced without air support and their arty was still heavily outnumbered. They reported Russia lost 25k kia, As always in wars bothsides exaggerrate losses of enemy so let's assoom Russia lost 50k total - kia, mia, refused to fight etc. I

This means Russia had about 100k vs 300k Ukrainians back then in the first line. So at the moment Russia lost 50k, Ukraine 150k. Also it might be 120k vs 360k or something like this, but it isn't that really important
If we assoom that Ukrainian numbers about kia were correct, it means that at that moment Russia lost about 100k in total. It can be true if Russia had more than 200k people, for example it brought some reservers and mobilization in Donbass republic was more comprehensive.

So losses of Russia before these events were 50k-100k, Ukraine 150k.


Winter

Ru base 200k + 300k mobilized + 50k Wagner = 550k
Ua base the same 600 k (actually more but we do assoomptions in favor of Ukraine)

25% support for Russia = 410k first line men
25% support for Ukraine = 450k first line men

Let's subtract losses of both sides before Ukrainian advances in Autumn
Ru 410k-50k = 360k
Ua 450k-150k = 300k

Russia slightly outnumbers Ukraine, but now Russian army is less experienced than in Autumn, as it has a lot of freshly mobilized men and convicts.

Ukraine doesn't advance anymore anywhere and loses ground even in heavily fortified zones. Russia tries to advance in multiple areas simultaneously, with mixed results. Ukraine now has more arty, Russia has problems with logistics of ammo.
So again, let's be generous for Ukraine and assoom Russia has 2:1 or even 1.5:1 superiority of the first line forces, it is barely enough, that's why many assaults fail, but Russia tries to attack as fast as it can before Ukraine gets even more modern weapons.

Let's assoom Russia lost another 60k men (unlikely but still)
Russia: 300k left on the front
Then Ukraine should have now about 200k first line men defending in the trenches and close reserves

Totals:
Russia lost 100-160k
Ukraine lost 250-300k with assoomptions favorable to Ukraine, so likely its mor, maybe up to 400ke.

The numbers should be correct with precision of +- 50 k