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Keeping tabs on your credit score can be difficult — especially if you don’t know what’s hurting it. The truth is that even seemingly small things can have a profound effect on your score.

Whether you want to increase your credit score, fix mistakes on the report or repair credit issues of the past, here are 20 things you need to know that can affect your credit.

1. Having Too Many Credit Cards

Keeping too many credit cards open at one time can be problematic, even if you pay each of them off monthly.

“Having too many cards can negatively impact both your credit score and your ability to borrow money,” said Julie Pukas, head of U.S. bank card and merchant services at TD Bank,

Even if you don’t tend to use all your available credit, lenders might wonder what would happen if you did max out your cards.

How to avoid it: “Having three to five credit cards is usually not a problem. But if you find your credit card balances are increasing, that’s a danger signal,” said Pukas, who advises limiting the amount of available credit you have at any one time.

How to fix it: If your ratio gets too high, you might consider closing one of your newer credit accounts to keep your utilization ratio low and your credit history long.

2. Closing Old or Inactive Credit Cards

While it’s smart to limit the number of credit cards you have at any given time, Pukas notes that closing old or inactive cards can come back to haunt your credit score.

“The length of your credit history affects 15 percent of your score,” she said. “This is why it’s important not to close credit card accounts that you have had for years.”

How to avoid it: Strive to keep older credit cards active by using them sparingly — once every few months — and paying off the balances on schedule.

How to fix it: “If you don’t trust yourself to put a card away in a safe place and not use it, then consider canceling newer accounts rather than old ones, so that the length of your credit history is not impacted,” Pukas said.

3. Making Late Credit Payments

U.S. News & World Report estimates that a single late payment can lower credits scores by 100 points or more. However, borrowers might be able to mitigate the damage, assuming they act fast. While missing a payment by just a few days likely won’t put your scores at risk, paying bills 30 or more days late can have a serious effect on your credit.

How to avoid it: If you paid a bill late, you can contact your lender to see what its policy is for reporting late payments. Some companies opt not to report late bills to collectors for 60 to 90 days. Unfortunately, if the lender has already reported the late payment, you probably won’t be able to get it removed from your credit report. You’ll just have to make sure all your future payments are made on time.

How to fix it: You should always check that the information your credit report is showing is accurate. According to the Fair Credit Reporting Act, credit bureaus are required to correct or remove inaccurate information. Start by sending a letter to the lender and each of the three credit agencies — Experian, Equifax and TransUnion — stating the date the payment was due and the date it was made. For best results, include all supporting documentation and an explanation of the error.

Read: The Easiest Way to Avoid Late Payments

4. Having Unpaid Parking Tickets

When a parking ticket doesn’t get paid on time, the city that issued the citation can opt to send the bill to a collection agency. Hence, a $35 expired meter ticket can turn into a $500 problem that will plague your credit history for years.

How to avoid it: Feed that meter and pay all your parking tickets on time.

How to fix it: If your unpaid tickets have already gone to collections, then you’ll have to deal with the agency in question to resolve the issue. Because collection agencies buy debt for pennies on the dollar, you can usually negotiate a lower price to mark the collection as paid. However, this doesn’t mean the information will come off your credit report — it can stay there for up to seven years.

In some cases, offering to pay a bill in full can prompt the agency to remove the debt from your credit report. If you want to go this route, draft a good will letter requesting that the lender remove the negative information as a kindness.

5. Having Overdue Library Fines

Believe it or not, a $5 library fine can have a negative impact on your financial health. While many libraries overlook these small fees, some cash-strapped institutions will actually send overdue book fines to collections.

How to avoid it: Many libraries offer e-book rentals straight from their websites, so you won’t have to worry about turning books in on time. If you still prefer to check out traditional books, set a reminder on your phone, so you know when it’s time to return your loaners.

How to fix it: If your library fines go to a collection agency, they might show up on your credit report. Your best bet to fix this credit mistake is to pay the collection agency and send a letter to the library begging forgiveness and asking them to remove the item from your credit report.

6. Not Having Any Credit Cards

Lenders like to see a long history of responsible credit use, and if you don’t have a card, you might not have much information to show. It might seem counterintuitive, but not having any credit cards can actually hurt your credit score just as much as having too many. Further, a limited credit history can impact your ability to do things like rent housing, set up utilities or even secure low insurance rates.

How to avoid it: If you don’t want to open your own credit card, consider asking a friend or family member to add you as an authorized user. You won’t have to use the card to get the benefit to your credit report — you’ll simply be piggybacking off the good credit habits of someone else.

How to fix it: Becoming an authorized user on someone else’s card can also help you repair your credit mistakes. Just make sure the person who adds you to a credit account is a responsible borrower. After all, his or her bad borrowing behavior can also show up on your credit report.

7. Co-Signing on Debt

According to Ian Atkins, analyst and staff writer at Fit Small Business, co-signing for your family or friends on their credit cards, car loans, residential leases or even cellphone plans can be a quick way to ruin strong credit scores.

“This can impact you negatively in two ways,” said Atkins. “First, that debt obligation can immediately show up on your credit report, and the higher debt load can impact your credit score. Second, if your friend or family member doesn’t make their payments, those missed payments will show up on your credit report. If the account eventually goes to collections, that too will show up on your credit report.”

How to avoid it: “You should be very careful when co-signing for friends or family,” said Atkins. “If you do co-sign, you need to 1) make sure you can cover the monthly payments if need-be and 2) that you closely monitor the account to make sure no missed payments occur.”

How to fix it: If you co-signed on another borrower’s debt, and it’s having a negative impact on your credit, see if you can get the other person to refinance the debt in his or her name only. If that’s not an option, you might need to suck it up and take over the payments.

8. Failing to Build Your Own Credit After Marriage

Consumers often neglect to consider the ways in which a spouse’s credit behavior could affect their own scores. While individuals maintain separate credit reports after marriage, if you and your partner share one or more joint accounts, any delinquencies are likely to impact both of you. Additionally, couples often make the mistake of relying too heavily on one partner’s good credit.

How to avoid it: If one spouse has better credit, the other might be inclined to let that person take on all the debt. However, borrowing money in only one partner’s name can leave the other spouse with a flimsy credit history that limits his or her ability to secure loans after a death or divorce. For this reason, it’s important that both spouses take on some amount of debt.

How to fix it: If your credit history is on the light side, consider taking out a credit card or loan in your name and making dutiful payments. Additionally, newly married spouses who changed their last names should review their credit records to ensure that all information was transferred accurately.

9. Having Too Many Credit Inquiries

Multiple credit inquiries in a short period can have a long effect on your record.

“Applying for credit too often is problematic for a variety of reasons,” said credit expert John Ulzheimer. “The first is the unwanted inquiries that will appear on your credit report or reports, and that’s where most people believe it ends. But the real problem with applying for credit too often is adding a bunch of new accounts to your credit reports, which lowers the average age of your accounts. That metric is actually more valuable than the impact of inquiries.”

How to avoid it: The current credit scoring system allows consumers to shop for similar types of loans, like auto financing, in a short period of time without the inquiries being reported as multiple applications.

How to fix it: As long as you manage your current credit accounts well, your credit score should bounce back within three months of your last inquiry.

10. Having Negative Records

“Generally, negative records, such as collection accounts and late payments, will remain on your credit report for up to seven years from the date of first delinquency,” said Pukas. “Paying off the account sooner doesn’t mean it’s deleted from your credit report. Instead, it’s listed as ‘paid.’”

How to avoid it: Paying your bills on time and keeping credit card balances low will help you maintain healthy credit records.

How to fix it: Unfortunately, it’s very difficult to remove negative records from your credit report.

“Of course, it’s smart to pay your debts, both to reduce the total amount of debt you owe and to show your willingness to repay your obligations. But expect the negative record to have some effect until it is purged from your report,” said Pukas.

11. Paying Your Rent Late

Paying your rent on time might not help your credit score, but paying late can certainly hurt it. If your landlord grows frustrated with your late payments, he or she can report you to the credit bureaus.

How to avoid it: Some landlords will allow tenants to pay half their rents on the 1st of the month and the other half on the 15th. This way, you can avoid paying a huge bill at the top of the month.

How to fix it: If you have gotten into the habit of paying your rent late, ask your landlord if you can change the due date. Choosing a date closer to payday could make it easier for you to meet your obligations. If the building owner won’t work with you, then you might have to find more affordable housing, get a roommate or even land a side job to increase your income.

12. Failing to Pay Bills

“The fastest way to hurt your credit scores, for a long time, is to start missing payments and go into default on your obligations,” said Ulzheimer. “It takes a full seven years for most derogatory items to be removed, although some remain for 10 years, and your credit scores will never be great while negative information remains on your credit reports.”

How to avoid it: Keep a close eye on how much revolving credit you use. If your credit utilization rate — the percentage of credit you have used compared to the amount available — is creeping up over the 30 percent threshold, then you might want to stop using the card until you can pay the balance down.

How to fix it: Find out how much credit you have available and how much you have used. Then, make a plan to pay down the balance. You can also try to request an increase on your limit in order to make your utilization rate seem lower.

13. Carrying High Balances on Your Credit Cards

Your credit utilization ratio accounts for nearly a third of your credit score. The higher the percentage of credit you use, the greater the negative impact on your score. Keeping your credit card balances low helps keep your score — and your bank account — healthy.

How to avoid it: “There is no absolute ‘right’ answer to how much of your credit limit you should be utilizing,” said Pukas. “What’s more important to note is that, if you’re carrying balances on credit cards that exceed 50 percent of the available credit, then you’re hurting your credit score.”

How to fix it: “Strive to get your total credit utilization under 50 percent first and then keep going. This is one of the fastest ways to increase your credit score,” said Pukas.

14. Having Charge-Offs

When a debt goes unpaid for a long time, the company that reported the unpaid bill might mark it as a charge-off, thereby indicating it was unable to collect the debt. Like other debts, charge-offs can have a negative impact on your credit score.

How to avoid it: Most debt types don’t get marked as charge-offs until they are four to six months late. If you have any outstanding debts, pay them quickly to avoid this kind of mark on your credit report.

How to fix it: Unfortunately, paying a charge-off doesn’t make the information disappear from your credit report. The item will stay on your record for up to seven years after it gets reported.

15. Having Court Judgments

Judgments are issues of public record that show up on your credit report and that can lower your overall score. Unfortunately, these debts can be tough to resolve.

How to avoid it: The best way to avoid court judgments is, of course, to pay bills on time. If the debt was settled long ago but is still on your credit report, you might want to consider contacting the court in question to confirm that it has updated the records.

How to fix it: Generally, consumers need to take their cases to appeals court if they want to reverse judgments.

“Judgments can remain on your credit reports for seven years from the date the judgment was filed,” said Ulzheimer. “Even paying a judgment won’t cause it to be removed. The only legitimate way to get a judgment removed is if it is vacated.”

16. Foreclosing on a Home

Along with suffering the pain and stress of losing their homes, people who experience foreclosure will likely see their credit scores drop. How much your score plummets depends on your credit history prior to the foreclosure and other factors. However, the effects of a foreclosure can stay on your credit report for up to seven years from the filing date.

How to avoid it: If you’re having a hard time paying your mortgage, call your lender right away. You might be able to get help through the Making Home Affordable (MHA) program or your state’s housing agency. Consumers should beware of foreclosure scams and contact the Federal Trade Commission with questions.

How to fix it: Repairing your credit after a foreclosure is a slow process. While foreclosure isn’t as damaging as traditional bankruptcy, consumers should expect to have limited access to credit for several years. Use that time to pay your bills regularly and keep credit card balances low.

Read: Is My Credit Score Good Enough to Buy a House?

17. Consolidating Debt on One Card

If you owe money on several credit cards, you might be tempted to consolidate debt by transferring all the balances to one new card. Not only can this lower the average age of your credit history, but it can also increase your debt-to-credit ratio.

How to avoid it: To keep your score from dropping, make sure the debt you consolidate doesn’t exceed 50 percent of the available credit on the new card.

How to fix it: Charge purchases to a few different credit cards and keep the debt-to-credit ratios of each below around 20 percent. According to the credit bureau Experian, individuals with consolidated debt might want to consult a nonprofit credit counseling company about participating in a debt management plan.

18. Having an Off-Balance Credit Mix

Your credit “mix” refers to the variety of credit types you have on your report and accounts for about 10 percent of your credit score. When you only have one type of credit on your report, such as credit cards, it’s likely your scores will suffer due to lack of information.

How to avoid it: The ideal credit mix varies, but a healthy balance might feature a credit card, a student loan, a mortgage and a line of credit. This diversity of credit shows lenders that you can manage several different types of credit in a responsible way.

How to fix it: If you need to improve your credit mix, try diversifying the types of credit you have by adding a new type to your profile. While credit scores might dip when you first open a new line of credit, you can rest assured knowing they will rise again after about five months of making regular payments.

Read: 7 Warning Signs You Need Credit Counseling Now

19. Carrying Medical Debt

“Medical debt can remain on your credit report for seven years from the date the medical debt originally went into default,” said Ulzheimer. “The good news, however, is that medical collections that have a zero balance are not considered by FICO and VantageScore’s newest scoring models.”

How to avoid it: While you can’t prevent medical issues from occurring, you can take steps to prevent them from impacting your scores. According to U.S. News & World Report, anywhere from 50 percent to 80 percent of medical bills have errors. If you receive a high medical bill in the mail, take time to review the information and identify any mistakes. If your bill is accurate and you can’t afford to pay, try negotiating the balance with a medical billing manager or ask the hospital if it offers a financial assistance program.

How to fix it: Talk to your insurance company.

“Medical debt that is in collections might eventually have to come off your credit report if it has been paid or is being paid by your insurance,” said Ulzheimer. “This is the result of a settlement agreement between the credit reporting agencies and the AGs from 32 states.”

20. Not Paying Your Taxes

If you don’t pay your taxes, the issue isn’t just between you and the government. When you owe back taxes, the government can place a tax lien on your property, an act that lowers your credit score.

How to avoid it: To avoid taking a credit hit and encountering hefty fees, aim to file your taxes on time each year. If you can’t afford to pay the balance, work with the IRS to set up a monthly payment plan.

How to fix it: If the tax deadline is approaching and you have yet to submit tax information, consider filing an extension. You can also work with a tax professional to repay back taxes before they affect your credit score.

This article originally appeared on GoBankingRates.

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