I bought a vacuum cleaner for a hundred and twenty dollars. Two days later it went on sale for eighty-five. The store would not refund the difference because I had already opened the box. That thirty-five dollars annoyed me enough that I set up price tracking for everything I buy online now.

Retailers change prices constantly — Amazon alone changes prices on popular items multiple times per day. Price tracking tools show you the price history so you know whether a “sale” is actually a deal or just the normal price with a fake discount tag.

CamelCamelCamel for Amazon

This is the best-known price tracker and for good reason. Paste any Amazon product URL and it shows you the full price history going back years. You can see the lowest price ever, the average price, and how often it goes on sale.

Set a price alert. Enter the price you are willing to pay, and CamelCamelCamel emails you when it drops to that level. I have set alerts for things I do not need urgently — luggage, a desk lamp, a kitchen scale — and waited. Eventually the price drops. Sometimes it takes two weeks, sometimes six months. If I did not need it immediately, the wait was worth the twenty to forty percent savings.

CamelCamelCamel also has a browser extension called The Camelizer that puts a price history chart directly on the Amazon product page. You see the graph without leaving the page.

Honey and Capital One Shopping

These browser extensions automatically test coupon codes at checkout. Honey is owned by PayPal and works on most major retail sites. Capital One Shopping does the same thing and also notifies you if the same product is available cheaper on another site.

Both are free because they earn a commission when you use them. The catch: they track your browsing. If that bothers you, CamelCamelCamel and manual coupon searches are more private. If the discount is worth the data tradeoff to you, these extensions regularly find codes that actually work — unlike the expired codes that show up in Google results.

The seasonal price calendar

Some product categories follow predictable sale cycles regardless of which retailer you use:

• Mattresses: Major sales on Presidents Day, Memorial Day, Labor Day, and Black Friday. Never pay full price.
• Appliances: September and October — manufacturers release new models and clear out the previous year’s inventory.
• Furniture: January and July — retailers clear floor space for new collections.
• Clothing: End of each season. Winter coats in February, swimsuits in August.

If the item you want falls into one of these categories, waiting a few weeks can save 20 to 40 percent without any coupon codes or price tracking. The calendar does the work.