You don't *have to* count calories. I'm not sure where that assumption came from?
But here's the deal...
If how you're eating currently, without exercise, is maintaining your weight... increasing your activity while maintaining said intake will obviously put you in a caloric deficit.
Same food in (putting you at break even) + increased activity = caloric deficit
So yea, theoretically you'll lose weight.
How fast?
Who knows.
Really depends on what you're doing in terms of exercise I suppose.
However, here's another idea...
When people start exercising, their hunger generally increases too and the net effect is increased calorie consumption. So if you're just winging it, things will less likely 'work.'
That doesn't mean it's not worth a try.
I'll also add that, as noted before, you don't have to count calories. You can create a 'rough draft' meal plan. Know about how many calories and macros it has, ball park. If that, along with your exercise, doesn't seem to be 'working', simply decrease portions slightly from before. Sure, it's not as accurate as counting calories and weighing food and has a higher chance of not working... but there's certainly more than one way of going about things and sometimes the generally optimal approach isn't all that optimal on the case-by-case basis.
Answer your question?