If your savings are below £10,000 your Pension Credit isn't affected.
If your savings are over £10,000 then the system assumes that each £500 (or part thereof) will generate £1 of income per week - although where anyone is expected to find an investment paying 10.4% p.a. in interest is beyond me!
For example, if you've got £13,200 in savings then the system sees that you've got 7 lots of £500 above the £10,000 limit (because the last £200 gets counted as a full £500), meaning that it's assumed that you get £7 a week in income from your savings (and thus reducing the Pension Credit top-up to your income by that amount).
https://www.gov.uk/pension-credit/eligibility