There are a lot of folders.
Bank statements, one folder per account. This includes ATM records and records of checks you write, but not for things that are tax-deductible (more on this later). I'm also keeping receipts from things I buy with cash here.
Brokerage/investment accounts, one folder per account. Keep statements that show purchases or sales of investments, and stock and bond certificates if you have them. This includes things like IRAs and mutual funds (you should have year-end transaction statements for the latter).
Credit cards, one folder per card. Receipts go here. I have letter-sized envelopes to put receipts into so I can staple one envelope of receipts to each statement once I check them off (after the statement arrives in my inbox). The exception is for tax-deductible stuff, which should go into this folder until you check it against a statement, and then reciepts for those go into the tax-deductible folder (again, more on this later).
Business expenses and things that will get reimbursed in general. This is all going in one folder, because really, how many different people/organizations will I need to get reimbursed by at one time? Receipts and stuff from this stay in this folder until I'm actually reimbursed, then they go to the bank statements folder (if it was a check or cash) or the credit cards folder (if that applies).
Tax deductible items. They all go in this folder after they've been checked off from a statement (credit card or bank). Receipts, 8283s (the form you need to itemize donations over $500), and records.
Tax returns, one folder per year. This includes W2s, 1099s, tax returns, tax forms, and "supporting documentation," whatever that last one means.
Memberships and warranties, as long as they are active. For me, this means IEEE, ACM, and suchlike; other things I can think of are things like gym memberships, cell phone plans, blah blah blah blah. Not really financial, but they cost money and you probably should keep 'em as long as you have that membership or plan around.
Important documents of life. Again, they're not financial, but should be filed anyway. This is stuff like...
- Your birth certificate
- College transcripts, if you have them
- Your current passport
- Social security card
Salary and job docs. Pay stubs, year-end pay stubs, performance reviews and letters, things pertaining to your bonus if you get one, copies of IP agreements, NDAs, and suchlike.
Insurance docs. One folder per policy, as you might predict; keep policies, literature, claim copies, and statements of reimbursement here.
Retirement/401(k) stuff. Plan statements, summary descriptions, quarterly statements, employee benefit documents.
Student loans. This (happily - thank you, Olin!) doesn't apply to me, but might to some of you; keep your loan agreement and monthly statements here. Yep, one folder per loan.
There were some other things relevant to people who had children and/or mortgages; I have neither, so I ignored those bits; I figured this would be enough folders for the time being.
Next: What to keep how long?