Like it or not, your life is dominated by numbers — how much you make, how much you spend, the size of your monthly mortgage payment. If you don’t know the numbers, you become a slave to forces you can’t control. But learn even a few basics and suddenly your financial future becomes clear. To help you on the way, we’ve found 10 numbers that everyone should know. Master this handful of figures and you’ve mastered your finances.

26% equals the return on investment you’ll get by paying off your credit cards

If a friend tipped you off to a GIC that was paying 26% a year, risk-free, you would be on the phone screaming, “Buy! Buy! Buy!” But the odd thing is that you may be ignoring an investment that is guaranteed to put at least that much cash in your pocket.

The investment comes in the form of your credit card balance. Pay off your outstanding balance and you’ll earn the equivalent of a 26% annual return on your money. No other investment can promise such spectacular risk-free returns.

Talbot Stevens, a financial educator based in London, Ont., explains the math this way. Most bank credit cards charge 18.5% on outstanding balances. So for every dollar of your balance that you pay off, you save yourself 18.5% a year in interest charges. Saving that amount is equivalent to getting a hassle-free return of 18.5%.

But the reward you get is actually even better than that. Remember that the dollars you use to pay off your credit card bill are after-tax dollars. To generate an after-tax dollar that you can use to pay down your credit card balance, you need to earn more than a dollar before tax. Most of us have to earn something like $1.30 before tax to have a dollar left after giving the taxman his due.

Stevens estimates that most Canadians in a middling tax bracket would need to find a GIC paying 26% a year to generate as much money after tax as they would gain by simply paying down their credit card debt. If you’re in the top tax bracket the return from paying off your credit card debt is even larger.

As you may have noticed, GICs are paying nowhere near 26% — a 3% payoff is more realistic. So the lesson here is stunningly simple. “The best investment that most people can make,” says Stevens, “is to get rid of their credit card debt.”

50% of your working income equals how much you need to have coming in each year to enjoy a nice retirement

Some mutual fund companies insist that to provide yourself with a decent retirement you should save enough money to replace 80% of your working income. Working backward from that figure suggests that many middle-class couples must save upwards of $1.5 million to avoid eating dog food in their golden years.

No wonder so many of us feel stressed. But if you’re already dining on gruel to put away enough money to meet the experts’ �argets, we’ve got great news. You can ease off on the starvation diet. “It doesn’t take all that much money to finance a good standard of living when you’re retired,” says Malcolm Hamilton, an actuary and worldwide partner with Mercer, the human resources consulting group.

Hamilton estimates most retirees can live nicely after they finish working on 50% to 60% of what they made while they were still going into the office. Why do you need so little? Because by the time you hit 65, you’ve shed the killer expenses of your 30s, 40s and 50s. You’ve paid off the mortgage, bid farewell to day-care bills, watched your kids graduate from university. You no longer have to save for retirement because you already are retired. Even taxes are lower because you have less money coming in.

As your expenses fall, the amount of money you have left to spend on yourself shoots upward. Hamilton calculates that a senior couple with a $45,000 household income have about the same amount of cash to spend on themselves as a typical young couple in their 30s with a $90,000 household income. Half the young couple’s pay is chewed up by kids, mortgages, retirement savings and high taxes on their — supposedly — high income. But for the retired couple, those expenses are distant memories. Even though they appear to be making far less, they’re living just as well.

4% equals how much of your initial portfolio you can safely withdraw each year after you retire

Many of us are overoptimistic about how much money we can withdraw from our portfolios in retirement. We assume that our portfolios will produce 10%-a-year returns, so we figure we can count on a $100,000 portfolio to throw off about $10,000 a year in income.

Ah, if only that were so. William Bengen, a U.S. financial planner, conducted extensive research to figure out how much money cautious investors could count on withdrawing from their portfolios if they wanted to ensure that their money would last for at least three decades of retirement. Bengen looked back at stock market history to calculate the withdrawal rates that would have allowed retirees to weather the worst financial storms of the past.