Two independent ways to estimate the same revenue
This calculates ad earnings two separate ways from the same traffic numbers, because AdSense's own reporting offers two different lenses on identical revenue. The RPM-based estimate is the simplest: (pageviews ÷ 1,000) × your RPM, the same "revenue per thousand impressions" framing AdSense itself reports. The CTR-based estimate instead models the click path directly - pageviews × click-through rate gives estimated ad clicks, and clicks × average CPC gives estimated revenue from those clicks. The annual figure simply averages the two monthly numbers and multiplies by 12.
Why give you two numbers instead of one
Because RPM and CTR × CPC are calculated from different inputs, they will rarely land on exactly the same number unless your assumptions happen to be internally consistent with each other. The gap between the two estimates is itself informative - a large gap usually means one of your input assumptions (RPM, CTR, or CPC) is off from what's realistic for your niche and traffic.
Why this is a planning tool, not a forecast
Every number out of this calculator is only as good as the numbers you put in, and real AdSense RPM and CPC vary enormously by content niche, traffic's country mix, device type, and ad placement - sometimes by an order of magnitude between niches. Use your own AdSense dashboard's historical RPM and CPC as inputs for a realistic estimate rather than a generic industry average, which can be wildly off for your specific site.