Why doesn't keep-empty ever win?

Because you're paying double-housing during the trip — current city full rent + destination accommodation. The math only works if (a) the trip is very short (1-2 months, where break-lease + storage costs dominate) or (b) sublet is illegal AND your lease is ending naturally so break-lease fee is $0. Otherwise, keep-empty is paying for a house you're not living in.

What's a realistic sublet recovery rate?

Depends on building rules and city. Major-city tech-friendly buildings (newer NYC luxury, SF SoMa highrises): 70-85% via Airbnb. Older buildings or co-ops with strict rules: 0% — sublet might be in violation. EU markets vary heavily — Berlin allows under specific conditions, Barcelona requires licenses, Amsterdam restricts to 30 days. Always check the lease language and local law BEFORE assuming you can recover anything.

When does break-lease become worthwhile despite the fee?

When the saved rent during your absence exceeds break-lease fee + storage + re-entry costs. For a $4,000/mo apartment with $8K break fee, 6 months of saved rent ($24K) easily exceeds the combined costs (~$11K + storage + re-entry). The crossover is typically around 4-5 months — past that, breaking is mathematically cheaper than keeping the apartment empty even before considering sublet.

How do I price the re-entry Airbnb risk?

Conservative: 1.5-2 months at full Airbnb rate in your home city. The risk: housing markets in expensive cities can be tight; finding a comparable apartment at the same rent might take longer than expected. SF/NYC at the wrong time of year (September school year start, May-July peak) could mean 2-3 months of $4-6K monthly Airbnb. Pad your re-entry estimate if you're returning to one of these markets.

6 Months in Lisbon: Keep the NYC Apartment or Break the Lease?

The Three-Option Comparison

You’re going to Lisbon for 6 months. You have a $4,000/month NYC apartment. The math:

Option	Total cost (6mo)	Logic
A: Keep apartment empty	$36,000	$4K rent × 6 + $2K Lisbon × 6
B: Sublet at 70% recovery	$19,200	$1.2K rent × 6 + $2K Lisbon × 6
C: Break lease + storage	$30,950	$12K Lisbon + $11K break-fee+move + $1.2K storage + $6.75K re-entry Airbnb

Option B wins by $11,750 vs option C and $16,800 vs option A. The arithmetic favors sublet for 6-month trips with strong sublet markets.

When Each Option Wins

The break-even shifts with trip duration and sublet recovery:

Trip duration	Strong sublet (70%+)	No sublet (illegal)
1-2 months	A or B (close)	A
3-6 months	B clear winner	A barely beats C
7-9 months	B winning	C catches up
10-18 months	B vs C close	C clear winner

The takeaway: short trips reward keeping a home base (B if legal, A if not). Long trips reward severing the apartment (C). The middle months are flat-ish — go with whichever has fewer logistics.

Where this scenario doesn’t apply

Pets, partners, dependents. Subletting with a partner staying changes the math entirely — the partner is paying rent, you can do option B with 100% recovery.
Furniture you can’t replace. If your apartment has irreplaceable furniture or sentimental items, storage cost during option C is more than the $200/mo line item suggests — emotional cost matters too.
Lease ending naturally during trip. If your 1-year lease ends in month 8 of a 12-month trip, option C becomes free (no break-lease fee). The math overwhelmingly shifts to C.
Rent-controlled apartments. In NYC, SF, LA, breaking a rent-controlled lease and trying to find another rent-controlled unit later might be impossible. The “savings” from option C is illusory if you can’t replace the deal.
Subletting via Airbnb. Even if technically legal, Airbnb subletting often violates lease language. Many tenants have been evicted for unauthorized short-term rentals. Verify your lease and your city law specifically.

What to actually do

Read your lease before assuming sublet is allowed. Look for clauses on subletting, short-term rentals, occupancy by non-tenants. NYC and SF buildings often have these.
Check city law on short-term rentals. Numbeo isn’t authoritative — your specific zoning matters.
For 9+ month trips, default to option C unless you have strong attachment reasons.
For 3-6 month trips with confirmed sublet rights, option B is almost always the answer.
Pad re-entry estimate by 50% if returning to a tight market (SF, NYC, Boston in academic-cycle months).
Pair with the Sabbatical ROI tool to see how housing decisions affect total sabbatical cost.

Open the Slow Travel vs Rent calculator → and run your specific months, rent, and sublet recovery numbers. The cheapest option flips at predictable thresholds — knowing yours saves $5-15K on a typical mid-length trip.