Waterfall chart pattern in Matplotlib

Introduction

A waterfall chart helps you see how a starting value changes step-by-step to reach a final value. It shows increases and decreases clearly.

To show how monthly sales add up to a yearly total.

To explain how different expenses reduce a budget.

To visualize profit changes from revenue to net income.

To track changes in inventory levels over time.

To display stepwise changes in project costs.

Syntax

Matplotlib

import matplotlib.pyplot as plt

# Define data
labels = ['Start', 'Increase', 'Decrease', 'End']
values = [100, 30, -20, 110]

# Calculate cumulative sums for bar positions
cumulative = [0]
for v in values[:-1]:
    cumulative.append(cumulative[-1] + v)

# Plot bars
for i in range(len(values)):
    plt.bar(labels[i], values[i], bottom=cumulative[i])

plt.title('Waterfall Chart')
plt.show()

You create a waterfall chart by stacking bars on top of each other.

The 'bottom' parameter in plt.bar sets where each bar starts vertically.

Examples

Simple data setup with positive and negative changes.

Matplotlib

labels = ['Start', 'Gain', 'Loss', 'End']
values = [200, 50, -30, 220]

Calculate where each bar should start to stack properly.

Matplotlib

cumulative = [0]
for v in values[:-1]:
    cumulative.append(cumulative[-1] + v)

Draw each bar at the correct position to form the waterfall.

Matplotlib

for i in range(len(values)):
    plt.bar(labels[i], values[i], bottom=cumulative[i])

Sample Program

This program shows a waterfall chart with positive and negative changes. Blue bars go up, red bars go down.

Matplotlib

import matplotlib.pyplot as plt

labels = ['Start', 'Sales', 'Returns', 'Marketing', 'End']
values = [1000, 300, -150, -200, 950]

cumulative = [0]
for v in values[:-1]:
    cumulative.append(cumulative[-1] + v)

colors = ['blue' if v >= 0 else 'red' for v in values]

for i in range(len(values)):
    plt.bar(labels[i], values[i], bottom=cumulative[i], color=colors[i])

plt.title('Waterfall Chart Example')
plt.ylabel('Amount')
plt.show()

Important Notes

Waterfall charts are not built-in in matplotlib, so you build them by stacking bars.

Use colors to show increases (e.g., blue) and decreases (e.g., red) clearly.

Label bars clearly so viewers understand each step.

Summary

Waterfall charts show step-by-step changes from a start to an end value.

They are made by stacking bars using the 'bottom' parameter in matplotlib.

Use colors and labels to make the chart easy to read.