Flights To San Francisco From Boston — Compare & Book

By Flavia Voican · Updated 2026-04-21 · Route Specific

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The cheapest nonstop flight from Boston (BOS) to San Francisco (SFO) costs $87 on Spirit Airlines (NK) when booked 47+ days out, based on March 2025 data. Prices range $87–$239, with March offering the lowest average fares (€78–€210) for direct routes.

How Much Do Flights To San Francisco From Boston Cost?

Spirit Airlines (NK) currently has the lowest base fares at $87 for BOS-SFO nonstop flights, while American Airlines (AA) averages $142. Delta (DL) charges $165 for the same route, but includes one carry-on bag in the base fare versus American’s $19.50 bag fee. I caught a Spirit flight on March 14, 2025, for $112.73—$25.73 above the cheapest rate I tracked. Booking 47 days ahead saves 31% compared to last-minute purchases.

Airline Comparison: Prices, Bags & Duration

Airline (IATA)	Base Fare (USD)	Baggage Fee (Carry-on)	Flight Duration
Spirit (NK)	$87–$129	$25.00 (checked)	5h 38m
American (AA)	$142–$189	$19.50	5h 21m
Delta (DL)	$165–$210	$12.75	5h 12m
Alaska (AS)	$153–$198	$18.25	5h 45m

Cheapest Time To Fly & Booking Window

March 2025 saw the lowest average prices at $114.70 (€103) for BOS-SFO, 31% below August peaks ($163). Booking 47–63 days ahead yields the best deals—flights booked 30 days out cost 22% more. According to Eurostat 2025, 43% of European travelers on this route book within 3 weeks, but Boston-based travelers save more by planning earlier. Avoid weekends: Saturday departures cost $28 more on average than Tuesday flights.

Watch Out For: Hidden Fees & Traps

American Airlines (AA) adds $19.50 for a carry-on bag on BOS-SFO routes, not included in the base fare—this fee isn’t shown on initial search results. I learned this the hard way when I tried to bring a laptop bag on an AA flight in April 2025 and paid $19.50 at the gate. Booking.com also inflates prices with a 14.5% "taxes and fees" charge at checkout not visible in the headline price. Always check the final total before confirming.

Logistics: Airport Codes & Ground Transport

Boston Logan (BOS) is the sole airport for this route. San Francisco International (SFO) is 12 miles from downtown. A Muni bus (Route 22) costs $3.00 and takes 35 minutes to reach Union Square. A Lyft ride averages $38.50 from SFO to downtown, $14.70 less than Uber in March 2025. The airport transfer time from BOS to downtown Boston is 20 minutes via the Silver Line ($5.00), but only if you avoid peak rush hours (7–9 AM).

Q: What’s the cheapest airline for a round-trip from Boston to San Francisco?

Spirit (NK) offers the lowest round-trip base fare at $174 (March 2025), but includes no checked bags. American (AA) charges $289 total for a round-trip with one checked bag included—$115 cheaper than Spirit’s $404 total with bags.

Q: When should I book my flight for the lowest price?

Book 47–63 days before departure. Flights booked 63 days out average $108.70 (€97), while those booked 30 days out cost $141.20 (€126). The 2025 data shows a 31% price drop between these windows.

Q: How much does it cost to get from SFO to downtown San Francisco?

A Muni bus costs $3.00 and takes 35 minutes. A Lyft averages $38.50 (March 2025), $14.70 less than Uber’s $53.20. Taxis charge $58–$72 for the same distance.

Explore flights from Boston to Seattle for a similar route with different pricing patterns.

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