Sharpening blades

I’ve been skating for like 15 years more or less seriously but I’ve never known how often should I sharpen my blades… sometimes I’m scared it hasn’t been long enough and that I’m paying for nothing and sometimes I know I should have went earlier. Sometimes I touch my blade to feel it’s sharpness but I don’t know what I should feel really… I skate twice a week and my biggest jump is axel… does any body knows ?