The 20-minute detour math: when a second store is actually worth it

Deciding whether to visit a second grocery store comes down to a simple calculation: is the money you'll save more valuable than the extra time and fuel you'll spend? For a typical 60-euro grocery list, a 20-minute detour to a second store is generally worth it if it saves you more than 5 euros. This calculation helps you balance convenience with real financial savings, ensuring your multi-store trip genuinely puts more money back in your pocket.

How to calculate your "time is money" threshold

Before you can decide if a second store is worthwhile, you need to understand the value of your own time. This is about what an extra 20 minutes is worth to you when you're grocery shopping.

Let's assume a few things for our Cologne-based shoppers:

• Average hourly wage (after tax): Roughly €15/hour. This gives us a baseline for the monetary value of your time.
• Average car cost: Driving for an extra 20 minutes (including driving to the second store and back, plus parking and walking) might add 5-7 km to your trip. At €0.40/km (fuel, wear and tear), this is an additional €2-€3. If you're using public transport or cycling, this cost might be lower, but the time investment remains.
• The "hassle factor": This is harder to quantify but very real. It's the mental load of packing up groceries, driving again, finding new parking, and navigating another store.

For a 20-minute detour, the "cost" of your time is:

• Time cost: (20 minutes / 60 minutes) * €15/hour = €5
• Fuel/Car cost: Let's use an average of €2.50

So, the total quantifiable "cost" of a 20-minute detour is approximately €7.50.

This means if your grocery list savings by visiting a second store exceed €7.50, then the detour is financially rational. If the savings are less, you're essentially paying more in time and car costs than you're saving on your groceries.

A Worked Example: Your €60 Grocery List

Let's apply this to a realistic grocery run. You have a list that totals €60 if you buy everything at your usual single store.

You use an app like Best Price Alert and discover the following:

• Option 1: One Store (Your Usual Supermarket A)
• Total cost: €60
• Time: 45 minutes (including travel and shopping)
• Fuel: €1.50
• Total "cost" (groceries + time + fuel): €60 + (€15 * 0.75 hours) + €1.50 = €60 + €11.25 + €1.50 = €72.75

• Option 2: Two Stores (Supermarket A for some items, Discounters B for others)
• The app identifies that by splitting your list, you can save €12 on the items you'd buy at Discounters B.
• Total grocery cost: €60 - €12 = €48
• Time: 45 minutes (Supermarket A) + 20 minutes (driving to B, shopping at B, driving home) = 65 minutes
• Fuel: €1.50 (Supermarket A) + €2.50 (Discounters B detour) = €4
• Total "cost" (groceries + time + fuel): €48 + (€15 * (65/60 hours)) + €4 = €48 + €16.25 + €4 = €68.25

In this scenario, by taking the 20-minute detour, your overall "cost" goes from €72.75 down to €68.25. That's a net gain of €4.50. You saved €12 on groceries and only "spent" €7.50 more in time and fuel, making the two-store trip clearly worth it.

What if the savings were only €5?

• Grocery cost: €60 - €5 = €55
• Total "cost" with two stores: €55 + €16.25 + €4 = €75.25
• Compared to the one-store cost of €72.75, you'd be spending €2.50 more overall for the "privilege" of saving €5 on groceries. In this case, the detour is not financially optimal.

This math reinforces the importance of knowing the exact savings before you leave your house. Casual multi-store shopping might feel like you're saving, but without comparing live prices, you might actually be spending more in time and fuel than you gain.

Making the decision easier

This calculation gives you a framework, but real life is messier. Maybe you genuinely enjoy the hunt for deals, or perhaps you value every minute of your weekend highly. The key is to apply your personal values to this equation.

Tools like Best Price Alert do this math for you instantly. Instead of you manually cross-referencing flyers and estimating travel times, the app presents the most cost-effective shopping plan, including a one-store option and a two-store split, alongside the exact savings. It calculates your best path, taking into account current deals and your chosen stores, so you can decide if the presented savings justify the extra legwork.

Ultimately, the goal is to save money intelligently. Knowing your own "time is money" threshold helps you make smarter shopping choices that truly benefit your budget and your schedule. The 20-minute detour is only worth it if the savings outweigh the cost of that time and travel for you.