You can get salary expectations per titles from places like Stack Overflow and Glassdoor.

Most hiring managers shouldn't offer "X% over your current salary" -- and you shouldn't look for that either. You should look at your experience, your capabilities and compare that with market rates for those.

If your current employer is paying you 20% below market rate, then this is an opportunity for you to reset to (or above) the market rate. But in this example, if you were to use your current salary as an input to determining your new one, you'd probably still lose out.

The trickiest bit is mapping titles among different companies. The public salary data is usually indexed by title. You can probably come up with good estimates for which title you think makes the best sense for you.