Estimate subway fares by zones.
Zonal metro fares are built from a base fare covering the first zone plus a surcharge for each additional zone crossed, then adjusted for time of day. Crossing three zones therefore costs the base plus two surcharges, not three — the off-by-one is the commonest error when estimating a fare. Peak surcharges of 10 to 25% are typical on weekday mornings and late afternoons. Showing both the peak and off-peak fare makes the trade explicit: shifting a journey outside the peak window saves the surcharge every single day, which over a working month is usually more than any single ticketing choice you can make.
Subway Fare
Off-peak fare = base fare + (zones - 1) x per-zone surcharge; peak fare = off-peak x (1 + peak surcharge%); monthly = peak fare x trips per day x 21.7
Base fare for the first zone plus a surcharge for each extra zone you enter. A journey wholly within one zone pays only the base fare regardless of distance.
Usually if you travel more than about 18-20 days a month. Compare this monthly figure against the zonal pass covering the same zones — passes are typically priced at 30-40 single fares.