# Articles

## Why SUMPRODUCT?

In this article, I attempt to explain why you see SUMPRODUCT so often in formulas, and when you can use the SUM function instead. The short version: SUMPRODUCT supports array operations natively, which makes it very useful for solving seemingly unrelated Excel problems. In the current version of Excel, you can use the SUM function instead, but SUMPRODUCT is better for backwards compatibility.

## What is an array formula?

In the world of Excel formulas, the term "array formula" is probably responsible for more confusion than just about any other concept. This is because the definition of an array formula has become mixed up with the requirement to enter some array formulas in a special way, with control + shift + enter.

## Excel's RACON functions

There are eight widely used functions in Excel that use a syntax different from other functions in Excel. This syntax can make these functions more challenging to use, because it is not intuitive.  Read on for important information about COUNTIF, COUNTIFS, SUMIF, SUMIFS,  AVERAGEIF, AVERAGEIFS, MINIFS, and MAXIFS.

## Alternatives to Dynamic Array Functions

Dynamic Excel offers 6 brand new functions that solve hard problems in Excel like sorting, filtering, and working with unique values. For those not using Office 365, this page provides some alternative formulas that work in older versions of Excel.

## Dynamic array formulas in Excel

Dynamic Arrays are the biggest change to Excel formulas in years. Maybe the biggest change ever. This is because Dynamic Arrays let you easily work with multiple values at the same time in a formula. This article provides an overview with many links and examples.

## Excel Formula Errors

Formula errors are useful, because they tell you clearly that something is wrong. This guide shows examples of each of the 9 formula errors you might run into, with information on how to investigate and correct the error.

## How to lookup first and last match

If VLOOKUP finds more than one match, will you get the first match or the last match? It's a trick question. It depends :) This article explains this confusing topic in detail, with lots of examples.

## Excel formulas and functions

Most people never receive proper Excel training and spend years frustrated by the simplest tasks, especially tasks that involve formulas. To use Excel with confidence, you must have a good understanding of formulas and functions. This article introduces the basic concepts you need to know to be proficient with formulas in Excel.

## The double negative in Excel formulas

The double negative coerces TRUE or FALSE values to their numeric equivalents, 1 and 0. This is a useful technique in many advanced formulas that work with cell ranges.

## 101 Excel Functions you should know

Excel contains over 500 functions, with more functions added every year. That is a huge number, so where should you start? This guide provides a walkthrough of over 100 important functions in Excel with many examples and links. Click function names for details and more examples.

## How to use formula criteria (50 examples)

Criteria are a key concept in Excel, but building useful criteria for text, numbers, dates, times, etc. is hard because it requires a good understanding of how Excel handles data. This guide will help you build formulas that work the first time with over 50 examples.

## Excel shows formula but not result

Have you entered a formula, but Excel is not showing a result? This can be very confusing, and you might think you've somehow broken your spreadsheet. However, it's likely a simple problem. With a little troubleshooting, you can get things working again.

## How to use INDEX and MATCH

INDEX and MATCH is the most popular tool in Excel for performing more advanced lookups. This is because INDEX and MATCH are incredibly flexible – you can do horizontal and vertical lookups, 2-way lookups, left lookups, case-sensitive lookups, and even lookups based on multiple criteria. If you want to improve your Excel skills, INDEX and MATCH should be on your list. See below for many examples.

## How to make dependent dropdown lists in Excel

One of the most useful features of data validation is the ability to create a dropdown list that let users select a value from a predefined list. But how can you make one dropdown dynamically respond to another? In other words, how can you make the values in a dropdown list depend on another value in the worksheet? Read on to see how to create dependent dropdown lists in Excel.

## Excel Data Validation Guide

Data validation can help control what a user can enter into a cell. You can use data validation to make sure a value is a number, a date, or to present a dropdown menu with predefined choices to a user. This guide provides an overview of the data validation feature, with many examples.

## Formula to list weekends only

Sure, you can use a complicated WEEKDAY formula to generate a list of weekends. But with WORKDAY.INTL, you can do the same thing with a WAY simpler formula. The trick is to use a special 7-digit "mask" to filter out all dates except weekends.