In general I'd say it's likely that your income will be lower in retirement because right now you're earning enough to pay your bills and save for retirement, while once you're retired you don't need to be saving for retirement anymore. Furthermore if you go into retirement with some of your savings in a taxable account or a Roth account, some portion of your withdrawals won't even count as income. So while you're working you'll often have an income higher than expenses, it's quite possible for your income during retirement to be lower than your expenses.
That said, a $20k taxable income isn't all that high. I think it's relatively likely that you might end up in the same tax bracket during retirement that you're in now. If this is the case, you could benefit from some tax diversification: if you have all your savings in traditional retirement accounts, maybe consider contributing to Roth next year at least up to the top of your current tax bracket.