MileAnchor

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Last updated: August 30, 2026

A mileage log is only as good as the numbers in it. This page explains, in plain English, how MileAnchor detects your drives, how it measures distance, how miles become dollar values, and what the app does when the real world gets messy. If an accountant, employer, or auditor ever asks how a figure was produced, this is the answer.

How a drive is detected

MileAnchor watches for several independent signals that a drive has started:

• Your car's Bluetooth or CarPlay. If you register your car in Settings, the moment your phone connects becomes the earliest possible trip start. This is the strongest signal, because only your car produces it.
• Motion. Your iPhone's motion chip recognizes automotive movement and wakes the app, even when it isn't running. Because the chip needs sustained driving before it decides you are in a car, the first part of such a drive happens before tracking starts; that stretch is measured back to where the car was parked rather than being lost.
• Location changes. Significant movement detected by iOS prompts the app to check whether you are driving.
• Charging. Plugging into car power corroborates the other signals, but only alongside a motion reading from the last couple of minutes, so charging your phone at a desk cannot start a trip.

Two things sharpen the end of a drive. If your registered car disconnects, the trip is treated as finished at the moment the engine went off rather than whenever you next stop moving. And if the motion chip reports you on foot with no car connected, that counts as having arrived, so walking across a car park is never added to the drive.

A trip ends after roughly two minutes of standstill, which distinguishes parking from a stoplight. You can also end any trip immediately from the live trip screen, and trips you end yourself are always kept regardless of length. You can record a trip fully manually as well; manual trips use the same navigation-grade GPS from start to finish.

How distance is measured

While a trip is active, the app records your position at the highest accuracy iOS offers for navigation and adds up the distance along the route you actually drove. The mini map on each trip shows that recorded route, so you can see exactly what was measured.

Real phones lose GPS sometimes: parking garages, tunnels, a phone deep in a bag. When that happens, MileAnchor fills the gap conservatively, in this order:

1. Road routing. The app asks Apple Maps for the road distance between the known points, and accepts it only if it is plausible: no shorter than the straight line between them and no longer than three times that straight line.
2. Conservative estimate. If road routing is unavailable, the app uses the straight-line distance increased by 25 percent, which studies of real road networks show is a cautious understatement of typical driving distance.

Every one of these fallbacks is deliberately conservative: where the app has to fill in a gap, it fills it low. A defensible log never claims miles it cannot support, and any trip's distance can be corrected by hand if you know the true figure.

Recorded GPS is a different matter, and worth being straight about. Distance is added up between position readings, and every reading carries a few metres of uncertainty that lands as extra length rather than cancelling out. In stop-start traffic, where each reading covers only a short hop, that can add up: on one there-and-back drive the same road measured 1.64 miles one way and 2.04 the other, against 1.8 from a maps app. On longer drives the effect is proportionally smaller, a few percent. So the fallbacks lean low while a slow, stop-start drive can read slightly high, which is precisely why the odometer check below exists.

What gets kept, and what gets discarded

• Automatically detected trips shorter than half a mile are discarded as noise, unless your registered car was connected at some point during the drive, in which case the bar drops to a tenth of a mile. The test is whether your own car was there, not which signal happened to start the trip first, so a genuine short drive is kept either way.
• Trips you end yourself from the live screen, and manual trips, are kept at any meaningful length: your explicit action means it was real, though movement below GPS-noise scale (about 250 feet) is still discarded rather than logged as a zero-mile trip.
• If a detected trip ends during a short stop and driving resumes within fifteen minutes, the segments are joined into one trip so a drive-through or curbside stop does not split your record.

How miles become dollars

MileAnchor carries the official IRS standard mileage rates as a dated schedule, including mid-year changes such as the one that took effect on July 1, 2026. Every trip is valued at the rate in force on the day it was driven, and rate updates never alter past years. Reports show the math per rate period, so a year that spans a rate change prints both lines.

• Business miles are valued at the IRS business rate and reported for Schedule C.
• Medical miles use the lower IRS medical rate, for Schedule A.
• Charitable miles use the rate set by statute, which the app does not allow to be edited.
• Reimbursed miles are valued at your employer's rate, which you maintain with effective dates, and are never mixed into deductions.
• Rental car miles are excluded from per-mile deductions, because the IRS standard rate applies only to vehicles you own or lease. The app tracks rental costs as actual expenses instead.

Anchoring the log to your odometer

Numbers on a screen are stronger when they reconcile to the physical world. MileAnchor prompts for odometer readings, compares logged miles against the change in your dashboard reading, and reports the share of real-world miles the log captured. Tax reports print the readings that bracket the reporting period. This is the cross-check an auditor asks for, and most mileage apps skip it.

Purposes, edits, and honesty markers

• Trip purposes are assigned by you. When the app suggests one automatically, from your route history, a time rule, or a saved place, the trip is visibly marked as auto-labeled, and your own choices are never overwritten.
• Distance or time edits flag the trip as edited.
• Costs estimated with fallback fuel prices are labeled as estimates and can be corrected.
• Reports carry a signature line certifying the log, and per-vehicle totals, because tax forms ask for them.

Honest limitations

No automatic tracker is perfect, and we would rather say so here than surprise you. GPS drifts in dense urban areas. Detection can start late if iOS has aggressively suspended the app, for example in Low Power Mode. A trip that never produced usable GPS cannot be measured and will not be invented. Where MileAnchor has to estimate, it estimates low, labels the estimate, and leaves the record editable. Where it measures, a slow stop-start drive can read a little high for the reason described above. Both are why every figure stays editable and why the odometer check matters: your log should contain your numbers, not our guesses.

Questions about any figure in your log: support@mileanchor.com