Try this tool https://turbotax.intuit.com/tax-tools/calculators/taxcaster/?s=1. Enter your regular income first to see the regular tax. Then add the sale to see the effect.
Enter the difference between the sale price (less expense of sale) and what you paid for it originally as a long term capital gain (LTCG). Enter the depreciation you've taken over the years (depreciation "recapture") as other income. Depending on how much total income you have LTCG are partially taxed at 0%, 15%, 20% and/or 23.8%. Depreciation recapture is taxed at your marginal rate, but not more than 25%.

For a detailed write up on this complicated topic see https://ttlc.intuit.com/questions/2593356-sale-of-rental-property-in-2014. You may want to use professional tax help when the time comes, although TurboTax can handle it