Try to be accurate when estimating your mileage
Insurance is about risk and to work out an accurate premium, your insurance provider needs to know as much as possible about you and your driving habits. If you make a claim and your insurance provider discovers your mileage estimate wasn’t accurate, they might decide not to pay out.
If you’re deemed to have knowingly misled your insurance provider in order to get cheaper car insurance, then you could invalidate your policy. You may also find it difficult to get cover in the future with mainstream providers and, if you do, your premiums could be very expensive. Honesty really is the best (and only) policy when it comes to insurance.