The range is wide because the price is set by risk. Two people with the same loan can pay very different premiums, and some of the difference is inside your control.
Rough figure: 0.3% to 1.5% of the loan amount per year, divided by twelve. On a $300,000 loan that is roughly $75 to $375 a month.
Your monthly statement should itemize it, often labelled mortgage insurance rather than PMI. It also appears on the Closing Disclosure from when you bought. If you cannot find it, your servicer can tell you in one call.
Do not estimate when you can look it up — the range is wide enough that a guess can be off by a factor of three.
Nothing, for you. PMI protects the lender if you default. It exists so that lenders will write loans with less than 20% down, which for most buyers is the difference between owning and not owning. That is a real benefit — but the premium itself gives you no coverage.
Which is why cancelling it as early as you can is worth the effort. The payment is pure cost with no return.
See your own dates
Enter your loan and get all four cancellation routes with the date you qualify for each.
Improve your credit before applying. If you are still shopping, a higher score at application lowers the premium for as long as you carry it.
Ask about single-premium PMI. Some lenders let you pay it in one upfront amount instead of monthly. This can cost less overall if you keep the loan a long time — and more if you sell or refinance early.
Ask about lender-paid PMI. The lender covers the premium in exchange for a higher interest rate. There is no monthly line item, but the higher rate applies for the life of the loan and cannot be cancelled at 80%. That trade is usually worse than it sounds.
Cancel it as soon as you qualify. The cheapest PMI is the PMI you are no longer paying. For most homeowners this is the lever that actually matters.