Fair Usage Policy (FUP) Throttle Impact Calculator

Why broadband plans come with a Fair Usage Policy

Many broadband plans are sold as "unlimited", but the small print often includes a Fair Usage Policy (FUP): a monthly data allowance after which your ISP slows your connection to a much lower speed. Providers use FUP limits to stop a small number of extremely heavy users from consuming a disproportionate share of network capacity during peak hours. It is a middle ground between a truly unlimited line and a hard data cap — you are never cut off or charged overage fees, but your speed can drop from 100 Mbps to 2 Mbps without warning. FUP clauses are common on cable, DSL, fixed wireless, and even some fibre plans, especially in markets where wholesale bandwidth is expensive. The problem is that most customers discover the limit only after the throttle hits — usually in the middle of a video call or a game night.

How this calculator finds your throttle day

The calculator needs five numbers: your advertised plan speed, your FUP data limit, the speed your ISP gives you after the FUP kicks in, your average daily data usage, and the length of your billing cycle. It multiplies daily usage by cycle length to estimate your total monthly consumption, then divides the FUP limit by your daily usage to find the exact day your limit is exhausted. Days before that day run at full advertised speed; days after it crawl at the throttled speed. From there it computes your speed drop as a percentage, your effective average speed across the whole month, and translates the throttled speed into a streaming verdict — whether 4K, HD, or even 480p will still work. Everything updates live as you type, so you can test scenarios like "what if I cut my streaming to 1080p?"

Worked example

Take a 100 Mbps plan with a 500 GB FUP limit, a throttled speed of 2 Mbps, usage of 20 GB per day, and a 30-day billing cycle. You use about 600.0 GB a month against a 500.0 GB FUP limit, so your FUP limit is hit on day 25.0 of your cycle — the last 5.0 days run at the throttled speed. Speed drop: 98.0% — from 100.0 Mbps down to 2.0 Mbps. Effective average speed for the month: 83.7 Mbps. At 2 Mbps, 4K streaming is impossible after throttling — even basic HD will struggle, so expect buffering on anything above 480p. Verdict: FUP bites — the last 5.0 days of your cycle crawl at 2.0 Mbps. A plan with a bigger FUP limit would cost less than the frustration.

Practical tips to dodge the throttle

First, find out your real FUP limit — check your ISP's app or the contract document, because sales pages often bury it. Track your daily usage for a week; most routers and ISP apps show this breakdown. If your ISP offers unmetered night-time data, schedule big downloads and cloud backups for those hours. Dropping your default streaming quality from 4K to 1080p cuts data per hour dramatically and barely shows on smaller screens. If you keep hitting the limit, compare a higher-FUP plan against any FUP-free add-on your ISP sells — a full plan upgrade sometimes costs less than the add-on. And if your throttled speed sits below 5 Mbps, queue big downloads overnight rather than fighting buffering during the day.