Here are 20 financial things everybody should know but too many of us don’t.

1 The average credit card rate is 18.9%, but they vary from 0% to more than 50%. If you are paying off your debt, it’s not a problem. If not, you need to know your rate so you can see whether you can get a better deal.

2 How long your savings would last if you could not work. Ideally, you would have a six-month cushion, but for the average Briton it’s just 19 days, according to Legal General. That’s not necessarily a problem as long as you have something else in place to kick in when you run out of cash. To arrange that, you need to know how much you have.

3 What your home contents insurance covers. A standard contents policy will cover, say, an iPhone stolen during a break-in, but not if you lose it on the train. If you want that cover, you need to make sure you opted in for personal possession insurance.

4 What type of locks you have on your windows and doors. If you put the wrong sort on your insurance application, your household insurer may refuse to pay any claim for burglary. Check what you have and that you are complying with your policy.

5 What factors affect your credit rating. Six out of 10 of us don’t know this, according to Aqua credit cards. Yet a poor credit score makes it difficult or even impossible to get a competitive mortgage, loan or credit card.

6 When you can claim your state pension. Most people expect to qualify at age 65, but that is steadily rising and younger people might have to wait until they are 68 or even older. Find out for sure here.

7 How much it costs to use your credit or debit card overseas. This could be more expensive than your realise. Most cards charge foreign transaction fees of 2.5% or more, says Matthijs Boon at Moneycorp, adding: “Withdrawing cash on your credit card from an ATM is even more expensive.”

8 Where all your pensions are. It’s easy to lose track of old company pensions, especially if you have worked for several employers, says Jason Hollands at IFA firm Bestinvest.

9 How much your jewellery is worth. Soaring gold and diamond prices could mean your bling is worth a lot more than you paid for it, Hollands says. “Your contents insurance may no longer be adequate to replace the items if stolen, so get a fresh value.”

10 Your annual mileage. Your motor insurer wants to know how many miles you drive each year when you buy cover, as the more miles you do, the more likely you are to have an accident. If you have seriously underestimate your mileage it could invalidate your policy if you make a claim.

11 You can get cheaper car insurance by adding your partner to your motor policy. “Our statistics show that motorists who have another named driver on their policy make fewer claims,” says Erik Nelson at insurer Aviva.

12 Price comparison sites aren’t always the cheapest way to buy financial products. “They don’t always have the best deal with each provider, and take a cut of the sale, adding to the cost,” says David Scrivens at discount broker Clubfinance. Always compare prices with a direct quote.

13 Consider buying income protection, which replaces your earnings if you fall ill and can’t work.

14 Shops are not obliged to give you a refund. Your rights are limited if you have simply changed your mind, says Jonathan Maskew at find-a-barrister service myBarrister. “Stores only have to give you a refund if the item is damaged, of poor quality or unfit for purpose.”

15 The phone number for your bank. If your debit card is swallowed by an ATM and you’re not sure if it’s coming back out, or you suddenly find you’ve lost your wallet, you will probably want to cancel it quickly. Make sure you know the number or have it plugged into your mobile phone.

16 Where your receipts are. If you need to make an insurance claim, you have a much better chance of having it settled quickly, and with the amount of cash you want, if you have proof of purchase for things. Keep receipts and know where to find them.

17 Which day direct debits and standing orders leave your account. This is the best way to avoid being hit with a hefty unauthorised overdraft fee as you can take action if you know you are going to end up with a shortfall one month. You might be able to move money from a savings account, or arrange an overdraft.

18 What time your local supermarket starts reducing things. Save money on your shopping by working out when the supermarket marks down food. This is usually towards the end of the day, but it varies according to the supermarket.

19 What the excess is on your insurance. This is the amount the insurer will expect you to pay towards the cost of any claim you make. You can cut your premium by voluntarily taking on an extra excess, but remember that you must also pay your insurer’s standard excess.

20 How much your home would cost to rebuild. If you own a property you need to provide this to buy buildings insurance. It’s not the same as the market value it’s usually less, so it’s better to know rather than paying for more insurance than you need.

Guardian News and Media 2013