Travel Data / WiFi Calculator
Estimate daily mobile data while traveling from streaming, maps, and social media habits.
Returns trip total in GB and compares SIM card vs roaming costs.
International roaming and data plan costs are calculated by comparing your carrier’s default roaming rates against alternative options (international SIM, eSIM, local SIM, or Wi-Fi calling). The math is straightforward, but the differences between options can be dramatic.
Default roaming cost formula: Roaming Cost = Data Used (MB) × Rate per MB + Per-Day Fee (if applicable) + Call Minutes × Rate + SMS Count × Rate
Daily roaming plan cost: Daily Cost = Day Rate × Number of Days
eSIM / Local SIM comparison: Local SIM Total Cost = SIM Cost + Data Plan Cost Break-even days = (Local SIM Total − $0) ÷ (Carrier Daily Rate − $0)
What each variable means:
- Per-MB rate — carrier default roaming without a plan; can reach $10–$20/MB — catastrophically expensive for video streaming
- Day pass — most major US carriers offer $10–$15/day international day passes that include your standard domestic allowance; best for trips under 2 weeks
- Local SIM — buying a SIM in the destination country; typically $10–$30 for 5–15GB; best for trips over 1–2 weeks
- eSIM — a digital SIM downloaded to your phone; available from providers like Airalo, Holafly, Nomad; no physical swap needed; prices similar to local SIM
Reference: cost comparison for 10-day European trip:
| Option | Cost |
|---|---|
| Carrier default roaming (1GB used) | $150–$500 |
| T-Mobile Magenta (international included) | $0 (included) |
| AT&T/Verizon International Day Pass 10 days | $100–$150 |
| Airalo Europe eSIM (10GB, 30 days) | $18–$25 |
| Local SIM at destination airport | $15–$30 |
Worked example: 10-day trip to France. Expected data use: 3GB. Phone calls: 30 minutes. AT&T plan.
Option A — AT&T International Day Pass ($12/day):
- Cost = 10 × $12 = $120; includes calls, texts, and data at domestic speeds
Option B — Airalo France eSIM (3GB for $15):
- eSIM = $15; calls via WhatsApp/Facetime over data = $0 additional
- Total: $15
Savings with eSIM: $105 for 10 days — pay attention to which apps your travel companions use for calling; if everyone uses WhatsApp or FaceTime, a data-only eSIM covers everything.