If you're thinking of trading in your old car for a new one, there may be no better time to do it than right now.

According to the National Automobile Dealers Association (NADA), the average trade-in prices of used small and midsized cars have risen an average of $500, or 4.3 percent, since January, and $300 (2.6 percent) just since last month. The value of a used, 2009 Toyota Prius has risen almost $2,000, or 12 percent, since January. The price of a 2009 Toyota Camry has risen almost as much; 11 percent or almost $1,500 in the same time frame.

That may make April a perfect time to trade for a new car, taking advantage of high trade-in values before they begin to drop, as NADA predicts. Of course, the other half of any trade-in equation is the price of the new car. According to various measures, new-car prices are also rising gradually, as automakers have reduced production to better match market demand, thus reducing rebates. That trend is likely to continue. So your best bet may be to strike while you can get as much value out of your trade-in as possible.

If you're thinking of trading in, Robert Smith, associate director of cars web products at Consumer Reports, says, "Shoppers should remain disciplined and negotiate based on vehicle price—as opposed to monthly payments—to get the best deal."

And as always, look at the long-term financial picture, factoring the full owner costs, not just the initial purchase price and fuel economy.

See our best new-car deals. And find the latest pricing information through our model pages.