By now, you may have heard a few "rules of thumb" when it comes to saving for retirement : Some experts say you need to save 10% of income every year, while others say 22% . But no matter whom you listen to, there's a big problem with following "one-size-fits-all" rules. Why? These rules were written for both men and women — and women need more. On average, women earn less , work for fewer years , and tend to make more conservative investments, which means they get lower returns.