In any situation where a business employee cannot significantly improve my experience by going beyond the minimum standard of service set by the employer, it is inappropriate to tip.  It is also inappropriate to ask for tips, even passively, by way of a tip jar.  Restaurant counter service, where you order and pay at the point of sale, and leave with your tray, is an example of this.<p>Never tip unless the employee is genuinely helpful to you, saving you time or labor beyond what you may ordinarily expect <i>their employer</i> to provide.  Do not tip at all if there is a service charge included on your regular bill.<p>If the employee is providing you with a one-time personal service or a prolonged but nonpersonal service in conjunction with a regular purchase, you tip 10% the total regular value of the goods, before discounts and before sales tax.  This applies to delivery drivers, taxicab or livery drivers, massagers, stylists, or tour guides.  Most tip-worthy services that improve the value of your purchase will call for 10%.<p>If the employee provides you with prolonged personal service, you tip 15%.  This is for something like restaurant table service, or golf caddies, or personal shopping assistants.<p>If you are requesting a service that is technically part of the employee&#x27;s job, but only tangentially related to the main paid service, tip what you would regularly pay for one drink in a social context, rounded to the nearest dollar.  If you drink coffees at IHOP, give $1.  If you drink Miller or Bud at the dive bar, give $2.  If you drink lattes at Starbucks, give $3.  If you drink caramel appletinis at a bar lit by blue LEDs and with bowties on all the bartenders, give $20.  This is what you give to porters per suitcase, hotel housekeeping per day, concierge per favor, valet per car retrieval, matre&#x27;d per non-snooty table-seating.  This is also an appropriate amount to give for a street busker&#x27;s performance that you enjoyed, or for a crowd-patronage subscription.<p>For a full standard deviation above and below the median quality of service, those are the only three numbers you need to know: 10%, 15%, and your personal fixed tip amount.  For quality between one and two standard deviations below the median, you subtract 5% from a variable tip.  For quality above one standard deviation above the median, you add 5% to a variable tip.  For service more than two standard deviations below median, you complain to the manager and give a reason why you are not tipping.<p>If you intend to be a &quot;regular&quot; at any establishment, it is acceptable to tip more than the standard amount when the employees can greet you by name, or remember your &quot;usual&quot;, but not until then.<p>Anyone advising you to tip 20% for median-level service, or 25% for anything, anywhere, does not have any idea what they are talking about--completely clueless.  The standard is 10% for delivery or buffet, and 15% for table service.  It already scales perfectly well with the menu prices.<p><i>Never tip with anything other than cash.</i>  Advice is not a tip.  Religious tracts are not a tip.