During your working years, you are turning your income to asset.  During your retirement years, you will use the asset to generate the income. 

If you are making 100k annually, generally speaking, you will need 70% to 80% of your current income during your retirement years.  Based on 75%, you need 75k retirement income annually to maintain your life style.  To produce 75k retirement income, you will need $1.875m asset, not including your primary residence.  This is based on 4% withdrawal guideline.  

If you have social security income $25k, then you can deduct this $25k from this $75k, that means that your retirement asset only needs to generate $50k annually.  Based on 4% withdrawal guideline, you will need about $1.25m asset to produce this $50k income.